Here’s a list of apparently-good games that I don’t own (for 360 unless otherwise noted):
The Saboteur
Velvet Assassin
Gears of War
Elder Scrolls IV – Oblivion
GTA IV – both expansions
Forza 3
Halo 3
Batman – Arkham Asylum
Borderlands
Star Ocean (and also Tales of Vesperia, if you’re still into japanese rpg)
LotR – Battle for Middle Earth 2 (must check if it’s online only)
Prototype
Castle Crashers
Psychonauts (Xbox) and Brutal Legend if that’s any good
Mini Ninjas
Spore (PC)
Final Fantasy Fables: Chocobo’s Dungeon (Wii)
Harvest Moon (Wii)
Quake Wars