Let me see, nostalgia is a pretty good RPG that is quite traditional.
Oh chrono trigger of course, it's one of the best rpgs of the snes era and definitely worth a try, especially because of the multiple endings.
If you're a fan of the pokémon games there's also digimon world ds and diimon world dawn and dusk. In which you fight with a max of 3 monsters at a time, but it takes A LOT of grinding so be warned. THere are also two new digimon games coming up, so you might want to see what that's all about when it's released
You can also try the dragon quest games for the ds. Although I haven't played it that much, I think they're are great games (especially the music, it's so epic)
A bit less serious is fossil fighters in which you excavate dinosaurs. Not to be confused with dinosaur king, it is a quite good game, but it can be boring after a while and it may be too childish...
Another upcoming game is golden sun Dark Dawn. Although it hasn't been released yet, it has proven to be a great RPG series on the gba with great graphics, so that's also worth a try when it is released.
A game that isn't really great and may not be your taste is lunar dragon song/lunar genesis. It was one of the first RPGs for the ds and you can definitely see that in the execution of the game. This game is really a hit or miss, so check it out if you can, but you don't have to love it.
ERm... I'm running a bit out of games, lemme see....
Oh there's also the Japanese medabot games for DS. They are really nice and the battles are in full 3D but the language barrier can be a huge problem. If you do want to see how it plays, you can take a look because battling itself ain't too complicated.
WEll there are quite a lot of RPG games, you can also at gamefaqs.com for RPGs on the DS. Link:
http://www.gamefaqs.com/ds/list-71