for me? Hmm....

Rainbow 6 3: Raven Shield
Starcraft: Ghost
Condition Zero (the single playe version of Counterstrike)
Halo 2
Zelda GC
Fable
Doom 3
Soldier of Fortune III (if it comes out)
Final Fantasy X-2
Tomb Raider: AOD

Edit: Can't believe I forgot Star Wars Galaxies AND Phantasy Star Online for X-Box. The latter will be what drives me to buying a X-Box live kit.

Those are all games I am extremely likely to buy, unles they are completely butchered and turn out poorly.