THIS GUIDE DOES NOT GUARANTEE VICTORY NOR DOES IT GUARANTEE GETTING A GOOD SCORE.
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Builds similar to this one never end well, unless you are facing complete total ******s, the enemy team will not allow you to put a lot of sustained damage on them. I found that playing him more as a ad caster with the capabilities of doing sustained damage works out best.Team 1 is Lane.
Team 2 is Jungle.
Lee Sin is a tanky ad caster. Midding is not suggested. He can dart in and out of battles with 2 conditional flashes. In either of my builds you become quite beefy. Hopefully I will release a jungling guide as well.

Pros
-2 Conditional Flashes
-Good Damage output to mid game with only defensive items
-Can push people around
-Shield allies and easy harassment
-Great Ganker
-Beefy (in my build)
Cons
-Flashes are conditional
-With no offensive items late game you deal no damage
-Melee

My Current Ranked Win Streak with Jungle Lee Sin

Build 1
Greater Mark of Desolation Armor penetration for extra damage.
Flat hit points for better durability
Cooldown reduction to put out more spells can switch with flat energy runes so that the full combo can be put out(mobafire didn't have flat energy runes listed at the time this was made)
Greater Quintessence of Desolation More armor penetration for more damage
Build 2
Greater Mark of Desolation Again armor penetration, he is an attack damage champion after all
Flat armor for being tanky
Magic resist per level as your magic resist doesn't scale naturally.
For extra hit points
Jungle Lee Sin
Flat attack damage for more damage and faster clearing.
Flat armor to take less damage from jungle monsters
Magic resist per level as you spend your first couple of levels in the jungle so flat magic resist would be useless
Flat attack damage for more damage
Flat hit points for more durability.

Build 1
Taking 21 points in offence for the extra damage and penetration, while taking 3 points in utility for less death time. 6 points in Defense for that extra edge in survival.
Build 2
Taking 21 points in defense for being that tanky beefy guy who never dies, and taking 9 points in offence just for that armor pen.
Jungle Lee Sin
Always taking improved smite.
Offensive jungle takes 21 points in offence.
Defensive jungle takes 21 points in defense.
I don't take any points in utility with the revamped mastery trees.

Increases attack speed after spell cast and 2 attacks after replenish, spacing out your spells while farming allow your energy to stay high and gives you good attack speed.
Main damage spell and chasing spell. Does direct damage followed up with a flash damage if you choose to activate it again. This spell reveals stealthed units or units in the brush
Spell that shields your allies, allied minions or allied pets. Dashing to get a better position or saving a teammate from death. Can be self cast and if cast again gives Life Steal and Spell Revamp. Great escaping tool
AOE Instant damage, if activated again slows attack speed and move speed of those hit. All units hit (including stealth) are revealed for the duration.
Kick target (knock back). Pushes enemy around or cancel a channeled spell (like Death Lotus)

Build 1
Maxing Sonic Wave for good damage output, grabbing 1 point in Safeguard and Tempest to have your full arsenal. Maxing Safeguard second for assisting in team fights as well as giving yourself durability. Tempest will be your one point wonder till level 14.
Build 2
Grabbing one point in Sonic Wave first for checking bushes and ranged damage, while maxing Safeguard will allow you to protect yourself, your ally, or a minion tanking the turret. Like the first build Tempest will be your one point wonder.

The skill combo for ganking is often Sonic Wave/Resonating Strike to close the gap and Tempest/Cripple to deal more damage and slow them. Basic attacks and repeats on the combo to finish off and using Safeguard/Iron Will to shield yourself, gain lifesteal or escaping if you cant kill them anymore. I use Dragon's Rage to finish them off, or to push them into my teammates, or away if they are dealing too much damage to them.
However I have found a better ganking combo, running in and using Tempest/Cripple to slow then landing the slow skill shot Sonic Wave/Resonating Strike will be easy due to the slow.

8 Wards are put at max radius to show you the relative distance to warding.
To see a comparison of Warding Range to Flash click HERE.

Wards

Sonic Wave / Resonating Strike

Safeguard / Iron Will

Tempest / Cripple

Dragon's Rage

I take Flash and Ignite as spells for both builds. Flash for the all purpose movement spell and Ignite to finish them off or reduce those with massive healing.
Smite is taken for jungling instead of Ignite.
Other Summoner Spells
A good option but requires you to remove your speed spell or damage spell. Already have a slow anyway.
Your Safeguard gives you lifesteal, there should be no need to take it.
As a beefy damage dealer it might be good to take this, however you are not an initiation tank so...
Safegaurd is on short enough of a cooldown to use it on minions to get across faster. But you can teleport gank people.
A good option, but you are tanky/beefy enough to take most harrasments without a problem.
No mana...
I likes to gets big
Supports should take this, your only support role should be shielding and knocking back.
Decent replacement for Flash
NOTE: YOU CAN SMART CAST WARDS NOW! MAKING HOPPING TO WARDS SO MUCH EASIER! Try it some day.

Build 1
This build focuses around being able to instantly heal up, and deal massive amounts of damage.
Doran's Blade-Decent stats for cost, good early game item
Mercury's Treads-Reduce crowd control effects, replace with Ninja Tabi if they have a lot of physical damage and crowd control effects are not affecting your team fighting capabilities.
Wriggle's Lantern-Never have to leave lane, also can jungle/counter-jungle if needed.
Hextech Gunblade-Even better sustain as spells heal now (if you don't use W)
Trinity Force-Improve total damage output by approx 3 times
Bloodthirster-Who doesn't like massive damage and more sustain?
Infinity Edge-More damage without the need to farm it!
Last Whisper-Improve damage output with nice armor penetration!
Build 2
Doran's Shield-Good early game survivability
Mercury's Treads-Reduce crowd control effects, replace with Ninja Tabi if they have a lot of physical damage and crowd control effects are not affecting your team fighting capabilities.
Warmog's Armor-Build up a great health pool, rush it so that the need for farming can be reduced later on.
Force of Nature-Increase survivability, grants greater movement speed
Randuin's Omen-Greater chasing capabilities, with decent tanky stats
Atma's Impaler-Converts health into the damage that is needed late game but not early-mid
Banshee's Veil-Blocks spells, and makes armor and magic resist approximately equal.


Jungle Lee Sin
Offensive build is the same as the lane build.
Defensive build is the same as the lane build.

Build 1
If you feel your cooldowns are good enough as they are take these for more damage output in battles.
instead of a if the opponents don't seem to have a lot of early damage or their early damage isn't physical damage.
You are squishier in this build, taking Merc Treads to lower duration of crowd control to greatly improve your survivability.
If you are doing well this will give quite a lot of attack damage and give a speed buff at max stacks.
Another one you ask? Why yes! It gives 100 attack damage at max and 25% lifesteal.
For magic resist, extra damage, and attack speed.
If you find that the enemy isn't building much armor, replace with this. Gives less damage but a has speed buff and attack speed buff.
Extra attack speed, gives you a "burst". Perfect counter to people like Jax who have high dodge stats.

Build 2
It gives an aura that helps your team, nice to have if you have a lot of team fights early on and you have no support.
Good magic resist, blocks a spell every 45 seconds. Gives decent hit points.
If you are doing well, or have a lot of ***its.
would be a good investment if most of the damage you are taking is physical. Replace
If they happen to use crowd control a bit too much on you, think of this as a cleanse.
Nice item with Area of Effect magic damage, works well with your Tempest which is Area of Effect damage with slow. If they have a lot of physical damage or melee.
If their team is reliant on basic attacks and they are killing you or dealing too much damage than you would like then Thornmail will relive some damage and reflect some back.

With either build I sometimes take Boots of Swiftness as some games I find that people run so much faster than I do (You know...those Attack Damage carries that take phantom dancers and boots)
I have also found out that his spells apply spell vamp (how did I not know this *facepalm*) so taking a would be good as it gives attack damage, ability power (for your Safegaurd), lifesteal (basic attacks), and spell vamp (for your Q, E and R ability).

Lee Sin doesn't need to avoid any items....well he does have to avoid those that give mana only stats, but you can grab a Manamune! It won't benefit you that much but you are Lee Sin.

Last hitting with Sonic Wave is easy, if it doesn't kill the minion you can cast Resonating Strike. Minions at low health can be hit with Tempest , stand in the middle of them for full effect. You can also you Cripple to slow the minion speed and attack speed so that your lane is pushed to some degree, as your minions will have more damage per second.

Red buff is great on Lee Sin, as you dash in and hit them a till they are dead, and using your spells to aid in damage. The slow from the buff prevents them from getting away easily. Taking the opposing red will hurt their attack damage champions.
Blue buff should be saved for someone with mana. If no one on your team has mana problems go ahead and take it. Taking the opposing blue can cripple their Magic Damage carry.
I mention stealing their buffs but remember they can steal your jungle as well!
Lee Sin can solo dragon without much of a problem with the shield and lifesteal he gives himself.

Remember to space our your spells with 2 basic attacks to take full advantage of Flurry
Start with small golems, using Smite on them after casting Safeguard / Iron Will as spell vamp applies. Taking a point in Tempest / Cripple and move onto the Wraith Camp. Start with Safeguard / Iron Will, and attacking the Blue Wraith casting Tempest / Cripple and continuing this combo. This is the basic combo when jungling Safeguard-2 Attacks-Iron Will-2 Attacks-Tempest-2 Attacks-Cripple-2 Attacks, then repeat till all the neutral monsters are dead in the camp. Move on to wolves. Then taking the blue buff and heading back to base to grab Boots. Then go Small Golem-Wraith-Wolf-Red-Golem-Wraith-Wolf. Jungle Finished!
Remember as a jungler your job is to gank enemies or relieve a lane from an ally. If an ally is in need ignore the jungle!
Here is a map of the route. The purple side is the same route I just didn't label it.

I mentioned in the Katarina guide that zoning is very important. Though you are melee you have a longer range than other melees with you Sonic Wave. Also with the 2nd build you will be so ridiculously tanky that it won't matter if you are melee. Here is a video on zoning seen on my Katarina build guide. Play Video /league-of-legends/champion/shen-48

1)As Lee Sin you have easy harassment. Land Sonic Wave on enemy champion or minion in range of champion. Cast Resonating Strike. Use Tempest and Safegaurd out.
2)Remember Safegaurd can be cast on a ward, mushroom, jack in the box, or even a pet.
3) Safegaurd shields your allies. Don't forget to cast it whenever you can to save someone or give a little protection to someone. Use it on your lane partner right before taking damage.
4)The target you kicked with Dragon's Rage will fly a distance and all target that get hit will get knocked up. You can use it to hit someone out of range of any of your spells.

1)You are energy based, where energy is not much of a problem. Cast spells whenever you want to harass.
2)If your opponent gets hit by Tempest and the Flash away from you, Cripple can still be cast to slow them.
3)Using Safegaurd on a ward /sight ward will reveal it.
4) Will return energy even if the attack misses, is blocked, or dodged.
5) Resonating Strike and Tempest will reveal stealthed champions who are hit by it. They also keep the Line of Sight of all units hit by it.
6)When the laning phase ends and all the team fights start occurring, grab an Atma's Impaler as quickly as possible if you are following the tankier build.
7) Safeguard's range is being reduced by 50 in the Xerath patch.
8) Sonic Wave/Resonating Strike's damage ratio is being reduced by 0.1 to each. 1.0->0.9. If both hit one enemy its 2.0->1.8. Xerath patch.

8/18/11-Started Making Guide ,Publish
8/19/11-Edit Items to Avoid/Situational Items Chapters, Added Jungling
8/20/11-Added Skill Range Demonstration
9/24/11-Changed Phantom Dancers to Trinity Force, Runes/Masteries minor changes, paragraph about them not changed yet
10/3/11-Mastery tweaks, rune changes
12/15/11-Changed stat picture to the new style, Changed summoner spells to match Season 2, changed item build for build 1
12/18/11-Updated Chapter "Items" to match the new item build implemented
2/18/12-Updated builds, added small section in intro about attack speed Lee Sin

Giving +20 Energy greatly improves the use of the full combo without using auto attacks, granting a more bursty type of feeling. This is however personal preference.
NOTE: Energy runes cost quite a lot and are only usable on 4 champions but they do maximize Lee Sin's potential
Also the Rune and Mastery choices let me take any of the 2 builds mentioned above without too much trouble. Letting me switch between the builds (in the middle of the game) when we need one or the other, or when the glass cannon build is working out as planned.