In case anyone else finds it convenient, here is a list of DS games mentioned in response to Kenny's question:
* Space Invaders Extreme 2 (Gui)
* Bowser's Inside Story (Greg)
* Picross 3D (Greg)
* Sonic Rush (Jon)
* Meteos (Jon)
* Radiant Historia (James)
* Professor Layton and the Unwound Future (James)
* Elite Beat Agents (James)
James also mentioned Ace Attorney series, but they are probably better bought in the 3DS collection.
Link to the NWR feature that James mentioned (30 best DS games):
http://www.nintendoworldreport.com/feature/26080/the-30-best-ds-gamesSome games that I believe weren't in either list, but that come highly recommended:
* Chrono Trigger - yes, it's a remake of the SNES title... but still a brilliant RPG worth playing
* Contra 4 - balls hard, but great fun too (and with great unlockables)
* Dragon Quest IV, V, and VI - more remakes of classic RPGs
* Grand Theft Auto Chinatown Wars - also available elsewhere, but made for DS and I'd argue best here
* Kirby Mass Attack
* Mega Man Zero Collection - maybe having each GBA original is better, but getting the full collection is a lot more convenient
* Trauma Center 2 Under the Knife - the first game was essentially remade for Wii, but I don't think this is available elsewhere
* WarioWare D.I.Y. - an oddball entry in the series that has you make your own games; definitely niche appeal, but if it's your niche it's incredibly interesting; even better if you own the WiiWare counter-part that allows your minigames to be played on the big screen
DS library is filled with gems, some hidden and some right out in the open. Although I'm happy with my 3DS console, I own far more DS games than 3DS and don't expect that to change.