I have a couple that I found surprisingly great (to me)-
- Crash of the Titans: I'm a fan of classic Crash Bandicoot games from the PS1 era. The DS version came as a surprise. I expected something crappy, but got a classic style game with some really nice graphics. It has one huge flaw though- short as shit. I can beat the game in under 4 hours. It's only got 4 main worlds with 2 levels and a boss each. There is a final level, but it's just one level and a boss. Underwhelming to say the least. If it were longer, it would have been much more awesome.
- Giana Sisters DS: This game has been out in Europe for a little while now, but has a US released planned sometime. It was originally a very blatant cloned that ripped off Super Mario Bros on NES designed for systems like Amiga and Commodore. Quite fun on its own. Now it has sort of a retooling on the DS, and is completely different. But it's actually quite a great platformer. It's a little easy compared to Mario, but it has a lot of heart. It has some nice 2D pixel art as well that reminds me of Cave Story a little. If you want a nice little traditional platformer that emulates Mario, you might like it. In some ways, it's actually better than New Super Mario Bros.
-Megaman Starforce 3: The Starforce series is kind of mediocre, until the 3rd game, which I personally believe is much better than the first 2. I don't even quite know why, but one reason is that you can just jack into wave form at will without wave holes, and just expands the series nicely. I still like the old Battle Network battle system, but SF3 really gave me hope for Megaman RPG's. It's not a bad little game at all, despite being a little childish.
-Pac n Roll: reminds me a little of Katamari, without the world enveloping parts. You roll pacman around levels using a trackball like control. It's quite nice, and one of the first DS game IIRC. I find it forgotten and underrated.