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.
3DS release dates from today's Nintendo Direct: • Mario & Donkey Kong: Minis on the Move (eShop exclusive, May 9) • Zelda: Oracle of Ages / Zelda: Oracle of Seasons (Game Boy Color, eShop, May 30) • Shin Megami Tensei 4 (July 16)