hah! nice - what DS did you get? and did you get a sammitch deal? (i ask cuz they might be cheaper now that 3DS just came out)
here are some of the must-have games (which you should be able to get pretty cheaply now; or even cheaper used off ebay or something)
Mario Kart
NEW Super Mario Bros
Grand Theft Auto: Chinatown Wars
Castlevania: Dawn of Sorrow
Castlevania: Order of Ecclesia
Castlevania: Portrait of Ruin
Legend of Zelda Spirit Tracks
The Legend of Zelda: Phantom Hourglass
Super Scribblenauts
Pokemon (any, if you like the genre - the new Black and White are likely the best)
Advance Wars: Dual Strike
Advance Wars: Days of Ruin
Picross DS
Animal Crossing: Wild World
