I'd recommend the two Mario Brothers RPGs (Brothers in Time, Bowser's Inside Story), as well as the remakes of Final Fantasy 3-4 and some of the Dragon Quest series. There is also a Shin Megami game on the DS that's pretty good, and The World Ends With You is a balls hard Square-Enix game. Contact is an interesting (it feels a lot like Earthbound, despite having a very different gameplay style) game made by Suda51 that you might find interesting too.
If your looking for stuff other than RPGs, I'd recommend the Professor Layton games, Elite Beat Agents, and Dragon Quest Heroes: Rocket Slime.
I've heard great things about Elite Beat Agents, I may pick that up, although since its a music game I cant play it at work which is where I'll do most of my DS gaming and I need to play with the sound off.
I took a look at The World Ends With You as per recommended, the gameplay looks awesome. Not sure about the art, its interesting, reminds me of Jet Set Radio art, but hey Square Enix makes good games so I'll be buying that one.
As for FF's, I know you guys love them, I've never played a FF game, ever. Mainly cause I cant stand the PSX and the entire PS franchise. I was going to play them back in the day when they were on the SNES but then they made the jump to the PSX and never came back (I never owned a PSX/PS2 so I missed out on a shit ton of FF's). I know they are each a self contained story right? But buying FF 3 or 4 without ever playing 1, 2 seems wrong
Right now my list to purchase stands at
The World Ends With You
Elite Beat Agents
New Super Mario Bros
Children of Mana
That should keep me occupied for a while.
Has anyone tried Golden Sun DS? I've got the 2 on the GBA, beat both of them, loved both of them. Is the DS one a 3rd game, like a sequel to 2? Or a prequel to 1? I just dont wanna rebuy a remake of them since I already own them in GBA form.
What about the Zelda games? Phantom Hour Glass? Spirit Tracks? Mario Kart?