3DS:
Super Mario 3D Land
Mario Kart 7
Shin Megami Tensei: Devil Survivor Overclock

DS:
Radiant Historia
Mario & Luigi: Bowser's Insisde Story
The Wolrd Ends With You
Inazuma Eleven
Final Fantasy Tactics Advance 2
Solatorobo
Ace Attorney series
Profesor Layton series
Ghost Trick: Phantom Detective

thanks for the many many suggestions, the also mentioned 'SMT:DS Overclocked' is a title i look forward to.. but it isnt announced for europe yet, while Abyss 3D is already out here. Life Suxx.

I googled a lot of the title's listed here, and my wallet will be bleeding, but i have to get a ton of games.. i get the feeling i missed out on a lot of great ones in the last years by not having a DS in my posession lol. ( the most interesting games, to me, are; The World Ends with You - simply because Nomura is involved lol, Golden Sun, Radiant Historia, Layton, Tactics Advance 2, KH, Nostalgia, Lufia, FF3, 999 and -- of course, Contra4. (i heard you Masschamber. =) a good challenge is a good thing for a change.)

The first games i'll get however, are Phantasy Star Zero (promised a friend - and since i played PSO for a loooooooong time, i tend to have affinity to this franchise.) and most likely OoT 3D.

HOLY SHEEAT, i want this Q_Q http://www.youtube.com/watch?v=qnqYQVrYzk8&feature=endscreen&NR=1

for the ds i recommend the world ends with you, phantasy star 0, fire emblem, ff tactics a2, and mario and luigi: bowsers inside story. i cant recommend 3ds games cuz i only have 2.

DS:

Elite Beat Agents
Ace Attorney series
Pokemon Black / White
Castlevania: Order of Ecclesia
Animal Crossing Wild World
Resident Evil DS
Hotel Dusk
Dragon Quest Monsters Joker
Contra 4
The World Ends With You
FF3 and 4 remakes

3DS:

Ocarina of Time 3D
Star Fox 64 3D
Super Mario 3D Land
Super Street Fighter 4

I kind of missed the Phantasy Star 0 on DS. I didn't even know there was one released. I enjoyed PSO (GC) back in the day so I might have to pick up a copy of that myself. Also, someone mentioned Pushmo (3DSWare) which I checked out a video on the shop channel yesterday. The game looked very promising for a puzzle game and I am probably going to have to pick it up. It looks like Nintendo has published a few pretty decent 3DSWare titles already. I've already bought Freakyforms but not sure if that would interest too many here. It can be considered more of a kids title but I am sure having some fun creating a bunch of weird characters.

THE WORLD ENDS WITH YOU for the love of all that is holy!!! Best JRPG released this gen IMHO
and Mario 3dLAnd is good too, better than i thought it would be

Cave Story. Either the 3DS or the DSi (download) version, though I recommend 3DS (better designed for the screen real estate). If you like Metroid series or Castlevania, you will like Cave Story.

Everything I was going to say has already been mentioned, so I'll second the people who said TWEWY, Inazuma 11 (and soon 2), the Pokemon RPGs, FF Tactics A2, as well as the FF/DQ remakes.

oh and Phoenix Wright is good, too. I got the WiiWare version though