Gotta say there's actually 5 games I'm really anticipating, though admittedly one of them has had very little info revealed and another has been merely hinted at. Anyway, they are as follows:
1. Left 4 Dead - An online, zombie themed, co-op game being developed by Valve. There's nothing in that sentence I don't like
2. Spore - It would seem that Maxis may have finally redeemed themselves, what with their rather lack-luster games in recent times
3. Mirror's Edge - Could be the new "Portal". As in, based on concept could be insanely fun and revolutionary or complete waste of code. Time will tell.
4. Portal 2 - I know nothing concrete, but they've already said, "More Portal is coming".
5. Half-Life 2: Episode 3 - A long way off I'm sure, but damn if the end of Ep. 2 didn't make me want this sequel even more.
Honorable mention: I have to say I find the idea behind Little Big Planet intriguing. Kind of like a mix of Garry's Mod and Ragdoll Kung Fu (not surprising, as LBP is created by the same guy that made RDKF). So, seeing as I own and loved both of those and there's proof of concept behind both, LBP could be extraordinarily fun. Too bad it had to be a PS3 exclusive. Kind of makes it loses some of it's appeal for me.