New Super Mario Bros - i think this is the one you're looking for
Animal Crossings - if u're into freeplaying (sandbox) games
Zelda: Phantom Hourglass - if u like RPG, buy this
Phoenix Wright - Find clues, contradiction, Objection!! (yaa u can even scream that on the mic)
Metroid Prime Hunters - great FPS for the DS...but hand will get tired
Castlevania - Side scrolling action rpg
Resident Evil: Deadly Silence - the original RE that came out on the PS1...now on DS. Same graphic, only this time have added first person view battle using the stylus.
Jam Session: if u want to play the guitar so bad but never had the chance ...oh yeah...a decent external speaker is a must if u want to enjoy this.