I know it may be blasphemous to mention this on a hardcore gaming forum but I actually really enjoy playing games on my cell phone these days. I much more often have 10-15 minute bursts of game time rather than the usual 30 min to a couple of hours needed to really get into a console or even handheld game.
The games I play the most are:
Cut the Rope. The objective is simple and innovative and makes for some really challenging puzzles. I also like how the mix it up with a new feature in each box.
Plants vs. Zombies. This is fun take on the tower defense genre with several different power ups to make each level a unique experience. This game can get pretty challenging too.
The Room & The Room 2 - This reminds me of those old school adventure titles where you must use the objects around you to solve puzzles. Both games are excellent.
What are your favorite games for the cell phone platforms? Anything you can recommend me based on my tastes?