I just got a Nintendo DS. Help me find sweet games to play.

Lurk:

The Phoenix Wright games are excellent. The story telling is decent and quite humorous at several parts. The puzzle-solving aspect is decent though a bit rough at times (there will be times where you'll just pick different items during a court case, finally pick the right one, and find that the actual item barely connects to the case without a lot of convincing by the main character). Note that these are becoming tough to find.

The New Super Mario Bros is also excellent. It is similar to its Wii counterpart. It brings back a lot of old-school Mario with a slightly new twist here and there.

The Legacy of Ys 1 and 2 are also nice. I played only the first game, but it is an overall easy game to get into. Well, if you're not me and go out into the world facing everyone without your sword anyway...

The Mario RPGs are also fairly good. I only played the first one a little bit but it felt decent. The second one is on my backlog. I have heard that one is more difficult. At least try the first one.

Mario Kart is pretty fun as well. Keep in mind that people will tear you up most likely in online play.

The Final Fantasy III and IV remakes are also decent. FFIII has lots of customization while FFIV does a nice job remaking the game.

Jam it back in, in the dark.