Talon is a powerful assassin who utilizes Attack Damage to the maximum. All his abilities and core strength relies on AD, and he is nothing short of a powerful offensive champion. This guide will be improved over time, so bear with me!

I'll attempt to do the best job i can in describing Talon's gameplay and how to work him best. Certainly, i won't be able to cover everything, and i won't be guaranteeing win (although my first two games have been insta-20 surrenders with me on top). If you have any questions, simply comment and i will attempt to get back to you ASAP (unless theres like 50 comments per day, then i might not be able to get back to you D: ).

Pros:

All attack damage.
Extremly powerful abilities.
Stealth, slow, silence, and damage over time that leaves a blood trail.
Great AoE damage.

Cons:

Squishy.
Low durability.
Very CC prone (exhaust ends all lifesteal and attack damage meaning a useless Talon).
Expensive build (i'd say bloodthirstier and IE combo is expensive for a non-jungler).

All in all, Talon is like a melee hybrid between Vayne and Katarina.

Obvious AD runes. Greater Mark of DesolationArmor penetration marks because of his Attack Damage reliability. Flat armor seals due to the fact he has no durability and relies only on stealth, timing, and lifesteal. Cooldown reduction because his abilities do a ton of damage and need to be utilized as much as possible. Attack damage quints for extreme early game damage.

With a Youmuu's Ghostblade, building Greater Mark of DesolationArPen quints is not necessary. Furthermore, Talon is not a champion that relies on attack speed, meaning that the current set of runes is basically the best way to go if you want to squeeze the most out of it.

Basic offensive 21/0/9, taking off all magic damage related masteries. I opt for more CDR then AS in order to eliminate any requirement for itemization towards CDR. The runes and masteries are enough for ~20% CDR, which will set you off on a good foot early game. The extra damage and attack speed allow a better flow of early game and most likely first blood. I personally dislike defensive spec or utility on Talon; his offensive game type requires the most attention to. By taking points out of offensive build, you're basically losing that extra damage which can save your entire game experience, especially (and mostly) in early game.

Still following the basic building of an offensive attack damage character, however quicksilver sash is a must. One exhaust and you are done for 100%, all your AD is nerfed and your lifesteal goes to 0. Also, magic resist never hurt anyone, especially against a Karthus. Crit strike is not an important key factor here because Talon is not a "Tryndamere of Assassins", but rather uses abilities and smart placement to put down good damage. Overall you're looking to maximize and squeeze out as much AD as possible while maintaining lifesteal, attack speed, and some type of durability (in our case the QSS).

Your Rake is a powerful farming ability, AoE slow, and AoE damage. A must at first level. At level 2, grab Noxian Diplomacy (using this ability on champions will make them bleed damage over time and force them to leave a blood trail for a few seconds). At level 3, toss a point at Cutthroat. From there on out, keep leveling Rake, followed by max Noxian Diplomacy and last Cutthroat, grabbing your Shadow Assault along the way.

When in a fight, use the following: Q -> E -> W -> R -> melee. Slows increase damage done by Talon, therefore don't attempt to melee until you've landed at least a Rake. I don't ult first because the daggers deal more damage if they pass through an enemy twice rather then only on the way back. Also, Noxian Diplomacy is applied with an attacked which is immediately following a Cutthroat, maximizing damage. The Cutthroat silence should keep your enemy as bay in order for you to throw down Rake and finish with Shadow Assault and basic attack.

Talon's ultimate can also function as an escape mechanism and as a stealth initiating/joining battle. The stealth and damage need to be utilized to the maximum. Remember, he does not retain stealth after the daggers have returned from his ulti.

Recommended choices:

Flash and your ulti go hand in hand. Easy escape from any sticky situation.
Exhaust for taking out the enemy AD carry or slowing down a chasing enemy.

Other viable choices:

Ignite... damage over time is excellent plus heal reduction, as an assassin that should insure a kill.
Cleanse so you can take off Quicksilver Sash and replace it with a Black Cleaver or some other Attack Damage item (however not recommended as you wont get any magic resist).
Teleport so you can easily pitch in on a gank or return to your lane quickly.
Ghost so you can book it out, run back in, or chase that sucker!!

Dominion Spells (can be found under Summoner Profile -> Spells):

When dominion comes out, i personally will grab the spell Garrison (Allied Turret: Grants massive Regeneration and Attack Speed for 8 seconds. Enemy Turret: Reduces Damage by 80% for 8 seconds) for easier map control. If you're being double teamed at a point, throw that sucker down and do your Talon work. If you're going for a point and get ganked in the process, throw that 80% turret damage reduction and kill or run like hell.
I don't recommend getting Promote because Talon is seriously not a support.

Not so great:
Clarity, Fortify, Heal, Clairvoyance, Rally, and Revive are all not the best choices for Talon. However, every single (i promise) spell can be used on Talon (or any other champion, seriously) and have some benefit to the team. Just because i or someone else is saying that isn't the best choice doesn't mean you have to let it go.
Think AD Soraka.

As i said in the intro, many more improvements to come!!! Talon is well balanced in my opinion and using his great abilities will maximize the ownage!

Oh and here are two screenshots to show you i'm not BSing about my stuff (both are surrenders at 20, i didnt have time to buy a B.F. Sword at the first game):


Image(s) by other player(s):

Image by jawzxz

August 25, 2011: Expanded the guide much much more. Removed ALL place holders, triple checked spelling and most grammar errors (after all this is just a guide, not an essay), and poked at Talon some more. Added screenshots and Dominion spells (bet you no other guide has that this early into the patch AND before Dominion is even out).

August 27, 2011: Revised guide language and wording some more, added a couple more images.