I've spent a lot of time in the past trying to make the most out of limited DS music software like Electroplankton and Jam Sessions (and even some homebrew stuff). Finally, somebody made a decent game, the Korg DS, and it's pretty much replaced everything else I've used. Here are some of the better tunes I've created:

- Hack (http://clarknielsen.com/music/ds/hack.mp3)
- Lunch Bit (http://clarknielsen.com/music/ds/lunch_bit.mp3)
- Hiding Like Flying (http://clarknielsen.com/music/ds/hiding_like_flying.mp3) (a remix of the Level 1 music from Stealth ATF for the NES)