Dead Rising is simply amazing, never before has it been so much fun disposing of zombies in so many various ways.
Crackdown, Online co-op storyline sandbox game= Heaven.
Rockstar table tennis (only like £4 in the UK so no doubt cheap as chips worldwide).
Condemned (Simply one of if not THE scariest games this gen).
And of course the usual suspects (Gears 1 & 2, Mass effect, Fable ect)
Great XBLA games for only 400 MS points (Streets of Rage 2, Ultimate Mortal kombat 3, Wolfenstien 3D, Sonic 1, 2 & 3)
Great XBLA games for 800 MS points (Rez HD, Ikaruga, Soul calibur, Outrun: online arcade, Duke nukem 3D)