This is my first guide, so please, bear with me.
Since his release I've been playing Talon non-stop, and have done fairly decent with this build after a little toying around with other builds. If you have any critiques or feel something should be changed, let me know. I'll gladly try something new and make changes as I see fit.

Talon's earliest memories are the darkness of Noxus' underground passages and the reassuring steel of a blade. He has no memory of family, warmth, or kindness. Instead, the clink of stolen gold and the security of a wall at his back are all the kinship he has ever craved. Kept alive only by his quick wits and deft thievery, Talon scraped out a living in the seedy underbelly of Noxus. His incredible skills with the blade earned him great notoriety. Various guilds sent assassins against him with a demand: join their ranks or be killed. His response was to leave the bodies of his pursuers stuffed in a dark corner or dumped in Noxus' moat. Having lived on the streets, Talon knew better than to waste - he claimed a blade from every failed attempt on his life, gathering a seemingly endless collection of weaponry.

The assassination attempts grew increasingly dangerous until one assailant met Talon blade-for-blade in a match of strength. To his astonishment, Talon was disarmed. He was facing down his executioner's sword when the assassin revealed himself to be General Du Couteau. The General offered Talon the standard of life that befitted an agent of the Noxian High Command in exchange for his allegiance. Talon accepted on the condition that his service was to Du Couteau alone, for the only type of orders he could respect were from one he could not defeat. Talon remained in the shadows, carrying out assassinations on Du Couteau's orders until the day that the general disappeared. Talon's suspicions led him to the doors of the Institute of War, where he joined the League of Legends in order to find the parties responsible for Du Couteau's disappearance.

"The three deadliest blademasters in all of Valoran are bound to the house of Du Couteau: my father, myself, and Talon." - Katarina Du Couteau

Pros

Great burst damage
Scales off AD
Decent CC
Stealth
Easy farming

Cons

Very squishy
Often focused
Few escape methods

Mercy - This is Talon's passive. Any unit under crowd control (Silence, slow, etc etc.) will have extra damage % done to them from Talon's basic attacks. Can be activated easily using Trinity Force or Frozen Mallet

Noxian Diplomacy - This is Talon's Q. On Talon's next basic attack he will deal bonus damage and cause the target to bleed, causing damage over time, leaving a blood trail, and being seen. This is maxed second.

Rake - This is Talon's W. It is a cone spell shooting 3 blades in front of him causing damage and slowing the targets hit. This will activate Talon's passive. Great for farming and harassing; this is maxed first.

Cutthroat - This is Talon's E. When cast on a champion, you will appear behind them, silencing them for a short time and causes your basic attacks to deal more damage. This is maxed last.

Shadow Assault - This is Talon's ultimate. During activation blades will be sent out in a circle around Talon, after a few seconds they will return to Talon, damaging all enemies hit going out and in. Talon is also stealthed during this time.

I start with an early Doran's Blade. It allows for some lane stability (which Talon can struggle with) early on, also giving some AD, useful for obtaining first blood.

Next I go for Boots, of course. I follow up with The Brutalizer. I feel that Mercury's Treads can wait until you have that done.

*Alternate for Merc Treads would be Berserker's Greaves for the attack speed, I found this useful, but some others may find Merc Treads more useful. Personal preference*

I finish up my Youmuu's Ghostblade and immediately go for Phage (after Vampiric Scepter) to allow more damage with Talon's passive.

Bloodthirster in my opinion is a must on Talon. He doesn't have much survivability in lane so this greatly increases that.

Here you have 2 options -
1. Finish your Phage by going Frozen Mallet
2. Finish your Phage by going Trinity Force
- I found going with Frozen mallet, due to it activating your passive on every hit.

To finish up my build I go with an Infinity Edge starting with B.F. Sword for the extra AD.

*End Game - If you're really struggling to stay alive, I suggest selling your doran's blade (if you still have it at this point) and buying a Banshee's Veil.*

Optional Items
Some people like to take Ionian Boots of Lucidity for the extra cooldown reduction. Personally I don't like this because I feel with Blue Buff (a great thing to have for Talon!) your CDR is already pretty decent.

Cloak and Dagger - This could be a good item to get if you're not going with Merc Treads. The tenacity will help you greatly, along with the extra attack speed.

Black Cleaver - As an assassin, you shouldn't be repeatedly attacking for the passive to take good effect.

Last Whisper - A viable option. Much better than Black Cleaver if you really need the armor pen.

Madred's Bloodrazor - Got a tanky team with a lot of health? Always a good thing to buy

Core Items

For runes I take common runes for a melee AD/DPS champion.
Greater Mark of Desolation - Armor Penetration is kind of self explanatory for a melee AD/DPS
Greater Seal of Armor - Allows for better lane presence and survivability
Greater Glyph of Magic Resist - Allows for better lane presence and survivability
Greater Quintessence of Desolation - Same as marks

Alternate Quints
Greater Quintessence of Health - Allows for better lane presence and survivability
Greater Quintessence of Attack Speed - Attack speed is always useful, especially for Talon.

Laning with Talon may be difficult for you if you decide to be risky about it. Remember, you're an assassin, so you don't want to jump right in there if you can't take anyone out.
Remember to harass and farm with your 'W' as much as you can. But also keep in mind that's a very easy way to push them back to turret, not really getting you anywhere you need to be. Your 'E' can allow for an escape, or even more harass depending on the situation, so remember to get a point in that at level 3!

Now you may be asking, "Why Exhaust over Ignite?"

Well there's a few reasons I prefer exhaust. First of all, it activates your passive allowing for a very easy first blood. Ignite just isn't as reliable. I'm sure you've had that time come where they have just a little bit of hp left and your ignite didn't finish them off, so aggravating!

Flash is just... flash. It's a great escape mechanic since Talon's only escape methods are his E and ultimate.

Alternates
Ignite - Of course you can always go for ignite, putting a point in your masteries for it, however I still prefer exhaust.

Teleport - Good for getting back into the action should you have to leave for some reason or another.

Ghost - Helpful for escape along with your ultimate, but I find juking with Flash a lot better.

Get any good games using my build? Send me a pic and I'll post them here!
^ We were getting absolutely dominated this round, in the last seconds it was between who could destroy the nexus faster.

^This started as a 5v4, our Malzahar came back in the last 5 mins, fed, and we lost.

Talon is a great overall champion. He's well balanced, with a great burst. You must remember though, he IS an assassin, so play him like one! Try to stay back in team fights and don't initiate. Don't take too many risks or you may find yourself dying a lot.
Hopefully this can be helpful to someone, please leave feedback!
Thanks for reading!

-Fox