Here's a few I can add:
Picross DS - this is my current addiction. If you haven't tried it you should! These are logic puzzles in which the process of solving them reveals a picture, which is a lot more fun then ending up with a grid filled with numbers (Suduko) if you ask me. Best to just try it and see. It comes with many puzzles built-in and you can also download more puzzles taken from past renditions of the games (such as Mario Picross). It also has a fun online competitive game. You can also make your own puzzles and (in theory) share them with others and download ones others have made, but doing that requires exchanging friend codes - if there was ever a case against friend codes, Picross DS is it.
Pac-Pix - this game is fantastic and makes great use of the DS touchscreen. It deserves much more notice on the DS and definitely deserves a place in your library. The game has you drawing one or more pac-men of different sizes and then walls to guide them around the playing area, as well as arrows and bombs in later levels, to hit switches and such, all in an attempt to eat up ghosts and other bad guys within a time limit. It starts out easy and gets maddeningly difficult and frantic in the later levels, with a nice difficulty progression. It's really fantastic and available for cheap.