Nah, I really think you should wait and get a 3DS once there's a price drop, but that's not what you were asking.
All the Pokemon games ( Main Series and Mystery dungeon ONLY)
The Mario and Luigi rpg series
Radiant Historia ( Awesome rpg with an interesting concept. Right up their with Shadow Heatrs and Chrono Trigger.
Dragon ball Origins 1 and 2 ( Don't be fooled, these games are fucking awesome!)
The Shin megami Tensei series ( preety much any game on the Ds. I think their only 2)
The Professor Layotn games ( Awesome puzzlers)
Phoenix Wright series
Elebits: The Adventures of Kai and Zero'
Dragon Quest series ( Get ready to lose your social life)
Super Scribblenauts
Sonic Rush
Sonic Rush Adventure
Sonic Colors
The Trauma Center series
Okamiden (I want it, but can't really get in to my Game Buying scedule.)
Mega Man Zero Collection ( About 4 games a cheap price, with some tweaks)
if you like Zero collection, get Mega Man ZX
Castlevania: Order of Eclasia ( my first Castlevania game. Its AWESOME)
Castlevania Dawn of Sorrow
castlevania: Potrait of Ruin
9 Persona, 9P Places, 9 Doors
The Legend of Zelda games on the DS
Kingdom Hearts 358/2 days ( STAY AWAY FROM RE:CODED!)
The World Ends With You
Fire Emblem: Shadow Dragon
The Kirby games
Mario Kart
Thats should last you your lifetime.