Disgaea for the DS. If you like srpg's, Disgaea is one of the bests. It's only 20 bucks at most places too, so you get a great and deep srpg with a very funny script for cheap.

You could buy it for the ps2 instead, but since you want games for the DS it's a good thing it's been ported.

I'm not sure if you're still looking for suggestions on new DS RPGs, but if you are...

Rune Factory 2: A Fantasy Harvest Moon

Final Fantasy IV

The World Ends With You

Chrono Trigger

Legacy of Ys: Book I+II

Mystery Dungeon: Shiren the Wanderer (WARNING! HARDCORE RPG AHEAD! You'll probably never beat it...)

Chrono Trigger, Final Fantasy IV, Dragon Quest IV, Dragon Quest V, The World Ends With You, Fire Emblem, etc.

Super Robot OG is another good RPG too ,not much complicate but battle system is good. :)

The DS has the best RPG library ever created. I'd recommend anything but The World Ends With You, since it's actually a turd disguised as a game! Would you believe they got away with that?!?!

forget the RPG, get Rhythm Heaven!!!

the dragon quest remakes are the best rpgs in the ds, the world ends with you is good but a little different from all rpgs.

Maybe Final Fantasy IV.

This game is evil. I love it so much. Evil, evil, evil! If they made popular games this way, TV sales would be through the roof because of replacement sets when everyone puts their controller through the screen.

I'm surprised nobody has mentioned suikoden teikreis yet. Pretty new, came out a couple months ago. It's the best RPG made specifically for the ds. Chrono trigger is of course a better game, but it is just a port from the snes.

Suikoden Teikreis is a great game that everybody with a ds and a love of rpg's should play.