Talon, is a pretty cool guy, I don't think anyone ever really reads introductions so here are the differences between the builds.

(If anyone could lend a hand, why can I not change this text's color?)
VVVVVV

Build 1:

Full glass cannon, you'll be insta-gibbing their carries but you're probably going to end up dying in seconds if you're not careful.

Build 2:

Safer to play, and preferred if you're going to mid against an AP caster.

Greater Mark of Desolation No question, these will have you hitting for true damage early game and scale great into late game.

Greater Seal of Armor Flat armor is great for going solo top. It helps to counter the current meta of 1 tanky-DPS top.

Greater Seal of Replenishment These combined with a Philosopher's Stone will have you raking all day.

Greater Seal of Scaling Mana Regeneration These have a higher turn-over at level 6, flat or scaling, both will alleviate most of Talon's mana problems.

Greater Seal of Attack Damage I don't like these too much, but the flat AD will allow you to Rake minions for more damage and if you get a fast The Brutalizer, you'll be able to one hit casters under your tower.

Greater Glyph of Cooldown Reduction Talon's damage is combo based, the more abilities you can use, the more damage you'll do.

Greater Glyph of Scaling Cooldown Reduction Scaling cooldown reduction, for those who don't like flat. However, at level 18, it will only make ~3% difference.

Greater Glyph of Scaling Magic Resist These are great if you're going mid against an AP caster, they scale great into late game and are still present early game.

Greater Glyph of Magic Resist These give ~13.5 MR and let you take less damage from Null Sphere or Sigil of Silence. They're great against early harassers like Kassadin or LeBlanc.

Greater Quintessence of Desolation More armor penetration!

Greater Quintessence of Attack Damage Again, flat AD helps with farming but armor pen will helps more against champions. Armor pen is generally better late game.

In this section, I will only be discussing the differences between the two trees.

Build 1: I take most of the standard AD masteries in the Offense tree, the only questionable ones are Lethality , Deadliness , and Vampirism . I take Lethality and Deadliness because I'm going to have more crit chance later and the +10% crit damage will make sure that they feel it. Vampirism is VERY questionable seeing as though Talon doesn't auto-attack much, you can substitue this for Havoc if you want, but I feel like Havoc is a bit under-powered right now.
I take Good Hands and Swiftness in the Utility Tree because Build 1 is a glass cannon build, you're going to die fast so this is the only real workaround we have. Swiftness is great to get you in range to let you Cutthroat.
Runic Affinity is mostly just for Red buff as your jungler should be taking most of the blues. Red buff is great for Talon as it procs Mercy letting you hit even harder.

Build 2: Again I take most of the standard AD masteries here. The only differences are Sorcery and Demolitionist . I take Sorcery here because I take MR glyphs instead of CDR. Demolitionist is great if you're going mid, as it allows you to down their mid tower faster (generally the most important tower). Again, feel free to substitute Havoc for Vampirism .
The nine points in the defense tree are based on countering AP mid. +6 MR +2 Armor, and +30-138 health will help you survive that Flash + Summon: Tibbers you know is coming.

Philosopher's Stone: After the nerfs to Talon's regens, I feel that this is really necessary for the staying power.

Youmuu's Ghostblade More armor pen! Some crit chance, cooldown reduction, and an awesome active! Although I generally forget to use this active unless I'm doing Baron or Dragon >.>

Mercury's Treads: Tenacity, so good. You can get Mobility Boots for better ganking but Tenacity is just too important to give up.

Bloodthirster: When fully stacked, it gives the most flat AD in the game.

Last Whisper: Even more armor pen! This lets you nuke tanks if you want! (not really)

Infinity Edge: This item I'm slightly fickle about, it still gives a ton of AD and stronger crits, but crits aren't all that reliable, and Talon normally attacks only once in his combo. Feel free to replace this with another one of Bloodthirster.

Trinity Force: This item will add greatly to you burst combo, your Noxian Diplomacy will hit like a truck on a bigger truck. Great for the added burst, replace this with another one of Bloodthirster.

Guardian Angel: This item is mostly just to look more intimidating, the particle effect makes people NOT want to focus you. If you do happened to get killed, make sure you Shadow Assault when you revive or you're just going to be killed again.

Quicksilver Sash: Great item, I always forget to use it but it's awesome against suppression ultimates like Nether Grasp.

Sword of the Occult: If you're on a smurf or you know you're going to snowball.

Mercy
10% more damage on CC'd targets with basic attacks. The damage is good but not enough to justify buying a Frozen Mallet. I am fairly certain that this stacks multiplicatively, so attacks to someone that's silenced and slowed will do 121% more damage as opposed to 120%.


This is you late game nuke. Early game, the extra damage isn't as noticeable. Note that this resets the attack timer and works on towers so you can take towers very quickly as Talon.


This is where your damage will be coming from early game. It farms minions so well and if you can hit your laning enemy, even better. This tends to fall off late game where Noxian Diplomacy will do most of your damage.

Cutthroat
This ability has so much utility, I've considered leveling this second just to lower its cooldown. It's an instantaneous blink and silence, but you need to target an enemy. The amplified damage really starts to show late game.
With this ability you can almost always get out alive if you're ganked, there's just so much this can do.

Getting chased by an explosive Icathian Surprise? Wait a little then Cutthroat to a minion and stab the poor thing!
Getting ganked by their jungler? Cutthroat to them and walk away while they cry because they're silenced!
Teammate about to get owned by Requiem? Cutthroat to Karthus (if he's still alive) and stab him!
Chasing Singed? Use Cutthroat to catch him then stab him!
Xerath marked you with Mage Chains and is about to blow his load? Cutthroat to him and stab him!
Wild Fiddlesticks appeared? Cutthroat away to a minion, or to him and stab him!
Getting out-stabbed by Death Lotus? Cutthroat to that Katarina and stab her!
Vladimir tower diving you? Cutthroat to him and Shadow Assault.Then laugh as he realizes he can't Trollpool out.
Malzahar staring at you intently? ( Nether Grasp) well... it can't get you out of that one. But there are so many options with this very versatile ability.


Shadow Assault, it sends blades flying everywhere and stealths you. This ultimate can be used to get out of the stickiest of situations. Just make sure you don't Flash while stealthed, otherwise, you'll break the stealth and look like a noob (It's ok to Flash early if they have vision). Did I mention it does awesome damage as well?
It's also great for baiting people into tower diving.
Note: You can close the blades while they're still moving outward if you attack, Flash, or Ignite. This is especially helpful for getting the damage in quicker.

Talon's skills hit extremely hard and have ridiculous AD scaling. The total AD scaling for all of his abilities totals to 4.5 damage per bonus attack damage. This doesn't count the damage amplification from Cutthroat. If we were to count this as well, it would amount to 5.055, not 5.175, because I'm only counting two ticks from the DOT on Noxian Diplomacy. Even so, 5.055 AD scaling means that for every 100 bonus damage you have (e.g. Stacked Bloodthirster), the total damage of your abilities will be increased by 505.5 damage. Include one auto attack (needed for Noxian Diplomacy) and it's 605.5.

Build 1: Max Noxian Diplomacy first. It does more damage than Rake and just one point in Rake can be used to proc Mercy. If however, you're facing someone like Morgana who pushes really hard or if you want to be more passive in lane, feel free to max Rake over Noxian Diplomacy.

Build 2: Here we max Rake over Noxian Diplomacy so we can push our lane harder.

I take one point in Cutthroat first because it is our blink spell and can really help against early ganks from Shaco or Lee Sin. If you don't feel like you're going to need a blink, you can wait until level 2 or 4 to take it. You can also take Rake first as the slow will also help against ganks.

First I must point out that you should ALWAYS LEAD WITH Cutthroat as it amplifies the damage of all your other abilities including Ignite.

Talon's combos require a lot of coordination, button-mashing will get you nowhere with him, and will just leave you frustrated.
(If you're playing Ryze of couse, just put everything on smart-cast and roll you face across the keyboard to win)

Noxian Diplomacy - Rake - Cutthroat - Shadow Assault

The Insta-gib:
Cutthroat + Ignite + Rake + Shadow Assault + Noxian Diplomacy.

Immediately cast Ignite after Cutthroat to maximize your damage (+5 AD from Summoner's Wrath ), then we Rake then Shadow Assault. While the blades are still flying outward, you attack your target with Noxian Diplomacy to immediately close the blades. While the DOT from Noxian Diplomacy won't be affected under the entire duration of Cutthroat it shouldn't matter as this combo provides the most damage upfront and you should have already killed your target.

You should use this combo on a caster who can CC you if they aren't silenced. It's aimed at nuking them before they have time to Zhonya's Hourglass or cast Terrify.
Note: You've done this combo correctly if you can cast Ignite + Rake + Shadow Assault + Noxian Diplomacy while they're still silenced.


Maximized damage:
Cutthroat + Ignite + Noxian Diplomacy + Rake + Shadow Assault

This combo is aimed at getting both DOTs from Ignite + Noxian Diplomacy under the effect of Cutthroat. You also end with Shadow Assault so you can wait and run away before you close the blades.

If you are really fast you can cast:
Cutthroat + Ignite + Rake + Noxian Diplomacy + Shadow Assault
To double proc Mercy.


Assassination:
Cutthroat + Ignite + Noxian Diplomacy + Shadow Assault + Youmuu's Ghostblade

This combo will kill the squishy and get you the mess you got yourself into. Wait until the blades close then use Youmuu's Ghostblade. Flash if necessary.


Harassment:
Cutthroat + Rake + Noxian Diplomacy

Just don't whiff your Rake. You'll look like a noob.


Endgame:
Cutthroat + Noxian Diplomacy

This is when everyone has full builds, you can nuke squishies with just these two abilities.

Quick note on Smart-casting:
Do it.

Team fighting as Talon can take a match or two to get used to if you've never played an assassin. You generally want to enter after the fight has started and clean up whoever you team didn't kill. Do NOT however, jump in after four of your teammates get obliterated. While Talon can escape many situations with Shadow Assault, you'll end up getting chain CC'd and die.

After your team initiates, you want to get behind the enemy tanks and kill the carries. Just remember that Cutthroat silences so don't be afraid to use it on Katarina during her Death Lotus.

If you end up using Cutthroat for the greater good and silencing a channel, use Youmuu's Ghostblade + Shadow Assault to run past the tanks and Rake the squishy. Follow up with Noxian Diplomacy. Just make sure you're behind them when you Rake so you can hit them with the second half of Shadow Assault.

Farming:
Rake + Rake + Rake + Rake + Rake + Rake
Can't Rake the minions fast enough? Get Youmuu's Ghostblade before Bloodthirster for more cooldown reduction.
Running out of mana? Level up.

Just a note about pushing. If you don't have a ward, you shouldn't be pushing. This changes however, when you get Shadow Assault, as it can get you out of most ganks, unless they have vision.

Ignite Talon is all about burst, this just adds to the carnage. It can get hectic, casting 5 spells in a matter of seconds, but if you've played Nidalee or Lee Sin, you'll have no problem coordinating yourself.

Flash Even after the recent nerf, it's still good, you just need to be slightly closer to the wall before you flash over.

Alternatives:

Exhaust: This is also a great spell to run on Talon It reduces armor, and slows the target, adding more damage via Mercy.

Ghost: For those who don't like Flash.

Cleanse: After the recent change to it, it's actually not half bad.

Smite: Necessary for jungle Talon.

Heal: If you can bait harder than a fisherman.

Clarity: Raking harder than a landscaper.

Clairvoyance: If you know what you're doing. Even then, it's very questionable.

Jungling as Talon is not recommended as it will screw up your late game.

Take Greater Mark of Attack Speed + Greater Seal of Armor + Greater Glyph of Attack Speed + Greater Quintessence of Attack Damage.

Start Cloth Armor + 5 Health Potions or Vampiric Scepter

Path: Wolves -> Blue -> Wraiths -> Wolves -> Red -> Double Golems.

This guide should not be followed word for word, it is just a recommendation on how to play Talon. This is how I play Talon, if you don't like it, don't downvote just because of my build or skilling order. There is no "correct" way to build a champion. You must adjust to the enemy's team composition.

Hoped you had as much fun reading as I had writing!
Happy stabbing!