Brain Training is a nice game, also tried the Maths Training, which was imo not as much fun but good for keeping the gray matter sharp

Then discovered Professor Leyton's Curious Village and got hooked to it. Really fun game to play and perfect for those quick pick-up moments when you've just a quick 10 mins to burn.
Then found Gravity on the DS, this is probably my favourite of the lot, simple but great game that does get trickier as it progresses.
[Only] 100 levels though, which I pretty much got through in a single sitting - Not wanting to put that game down. I need a Gravity 2.
Any other great puzzle games you've enjoyed worth checking out?