I don't know what you want, but...
Advance Wars

S. Awesome TBS game, even if you're not quite into the strategy thing.
Meteos: The first one is the best puzzle game on the DS. I don't know about the second one. It's Licensed by Disney and they took out some of the things that made the game so interesting.
Castlevania. Period.
Scurge: Hive. This is a sleeper title you can find for 10-20 US. There's almost no difference between the DS and GBA versions, though. Think an isometric Metroid.
Clubhouse games is fun, but there's a lot of filler. I recommend you get it cheap used if you can.
Magical Starsign is the best RPG on the system so far.
Tetris doesn't diappoint.