Deprogram offers us his homebrew "Rendezvous Delano, excellent Shoot Em Up" for the DS, based on the celebrated Metroid universe.
Since June, I've been working on a Metroid-oriented space shooter in PALib. Currently, it uses quite a selection of DS/libnds/PAlib features, including the following:
Music and sound effects via maxmod, including volume control
Rotating backgrounds
Changing background and sprite priorities
Rotating sprites (two different systems--16 pre-chosen rotsets and 16 available for more accurate rotations)
FAT saving/loading of options and saved games
Custom font
Both stylus and button-based controls
Wi-fi for checking for updates (but I didn't include the ability to download the actual update, although I possibly will eventually)
Dual sprites and normal sprites both
PA_GetAngle, PA_GetDistance, PA_CreateSpriteFromGfx (to avoid stability issues I originally had with PA_DeleteSprite)