Best Games I can get for under $13?

dark soul?

Sanctum? :D

Metro 2033

Defender's Quest, as it's one of the best TD games I've played. after the OMD serie, which you seem to have, but haven't played yet? go ahead and play them!

Bioshock, Witcher 2

Just cause 2 is $3.74, its an open world game. There is a multiplayer mod being worked on. I got it for PC mostly for the mod. (Also on your wishlist as I've just saw!)

Deus Ex

Payday: The Heist, on sale it's a steal, and it covers 3 of your 4 favorites: multiplayer, coop, shooter - as for tower defense not that much :P But it's a great coop game, if you're into L4D it's a no brainer to get this one. -----
never mind you already have it :D

Witcher 2, Alpha Protocol, Just Cause 2, DMC4, Wargame,

Critter Crunch! Best game EVAR.

PLAY THE DAMN ORCS MUST DIE 2!!!

Oblivion Goty Deluxe?

just cause 2, prototype, gta 4 complete edition, counter strike complete pack, terraria, payday the heist, bioshock, the witcher 1 or 2

For the Shooter category id suggest Black Light Retribution and it has a SEA Server and is FTP :D

The best "deal" you can get is by buying something from the holiday sale. If you play your cards right you can get three or four games for your $13.

Finish your games first and start them already! You have so many good games that you didn't start or played enough, and buying a new game would seem useless for you since you would just leave it there and never install after you purchased it.

FTL

The GTA Complete Pack is $12.49. Really good deal.

Plants vs Zombies.

Jamestown and Sine Mora are both fun if you like shoot'em ups.

Trine 2; Torchlight 2; Castle crashers; borderlands 2

Spec Ops: The Line is %75 off on greenmangaming, and if you use the code GMG30-DPLIM-DN831 you can get a 30% off extra, so you can get the game for $5.25

Red Orchestra: Heroes of Stalingrad 2, a very good game.

The Walking Dead > 12,49$ , from Amazon Digital Store (US, but you can buy it from abroad changing your adress)

Bastion, King's Bounty: The Legend, Puzzle Agent, Terraria, Trine, Unstoppable Gorg