So there are three things going through my DS right now
Trucking my way through Wario: Master of Disguise, and it's quite enjoyable. Really like the use of the stylus in this, though it can be tricky to master the subtleties between various symbols you need to draw. So far, I recommend!
Also am poking at Mind Quiz: Your Brain Coach. Perhaps I need to unlock more training modules, but my initial impression is to go back to Brain Age to get me my Sudoku fix.
The last one cycling through is Rayman Raving Rabbids DS, which is proving to be fun, but I think is ultimately more successful on the Wii. There are between-stage mini games, the first one being one of those heinous sliding picture puzzles. I detest these puzzles based on the fact that I'm terrible at them. However, after much pain, I got through it. The bad thing is, you can't bypass it. Fun, but I'm still seeing more play time with Wario right now.