Definitely Assassin's Creed III.
Maybe Dishonoured, if the reviews are good. The demo at the Eurogamer Expo didn't sell me on the game.
Also maybe Forza Horizon, again if the reviews say it's good. I need another racing game in my life, but Need for Speed: Most Wanted may be more to my appeal.
Honestly I'll probably only get Assassin's Creed III this month. I still need to get Mark of the Ninja and Tokyo Jungle.
Plus I have to save enough money for the games of next month!
Edit: Need for Speed: Most Wanted comes out in October in the US, but November in the UK. That's why I didn't say I'll be getting that game this month.