> Ive already got mario kart, mario and sonic at the Olympics, brain training,
> megaman starforce and space invaders extreme. Thinking of getting new track and
> field but other then that im struggling to see whats good

New Super Mario Bros, Kirby Canvas Curse, Phantom Hourglass, Ninja Gaiden, Contra 4, Castlevania Dawn of Sorrow, Final Fantasy IV, Tetris DS (if you feel like you don't own enough copies of Tetris), Brothers in Arms, Legend of Kage 2, Dragon Quest IV is coming soon, then DQ V and VI and IX some time down the road... Final Fantasy III is ok, but crazy grinding needed to kill that RPG. Get Mario 64 DS if you are a die-hard Mario 64 fan, it's very interesting... Trauma Center DS if you somehow avoided the Wii game...

Also get a homebrew cart and put ScummVM on there. That opens up a whole library of great games.