I've been on the fence for a PS3 Slim, so I'd start snagging titles like crazy.
But to actually name some I'll stick with what I have for now - xbox360
NHL10, Fallout 3 GOTY, Bioshock come to mind
And if I don't swing it at release, would be eyeing Borderlands and Brutal Legend
[I've preordered CoD:MW2, not sure how much game time/$ for more right now heh]