Left 4 Dead 2, first and foremost. Honestly, I'm giddy with anticipation. The more they reveal the more I find myself wanting it.
Besides that though, I really want to try Brutal Legend. Another game from the genius that made Psychonauts? Count me in. Then there's Tactical Intervention. A game being designed by one of the co-creators of Counter-Strike. It's essentially Counter-Strike 2 in that they added in features they weren't able to add into Counter-Strike: Source for fear of the players revolting.
Now, I was looking forward to ODST, but my God what a let down that turned out to be. Then there's Wet. Not perfect, not very polished, but damn surprising in how much fun I had with it.