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/DS Retail (Tuesday) • nothing 3DS eShop (Thursday) • Touch Battle Tank 3D ($4.99) • SALE: Super Mario Land 2 (Game Boy) is $2.99 until August 15 • CLUB NINTENDO: Golf (Game Boy) is 150 coins until August 12 DSiWare (Thursday)