I can only refer to the games that are also on xbox 360.
As mentioned Bioshock 1 & 2 were great if you like horror survival games, Fallout 3 & New Vegas are just friggin great epic RPG/shooter crossovers (mainly RPG) & Borderlands is all kinds of fun. The best game across platforms has got to be Red Dead Redemption though.
For something a little different and family appropriate, Ghostbusters is pretty great too. I bet you could probably get it pretty cheap.
In the latest addition to their AWESOME vs. series, Capcom brawlers will be taking on characters owned by the anime production company Tatsunoko. Their properties include G-Force, Speed Racer, and Samurai Pizza Cats. Here's a list of confirmed characters:...