I’ve been a long-time fan of Lumosity.com. Lumosity’s website features a suite of mind games that can be played quickly over your lunch break to keep your brain in tip-top shape.
Now you can take Lumosity with you via your iPhone or iPod Touch. According to this article at Mashable, Lumosity has released Memory Matrix and Speed Brain in the iTunes App Store. Memory Matrix is free for a limited time while Speed Brain will cost you a buck.
If you’re looking for a little more variety in your mobile brain games, you can also get Brain Challenge [iTunes Link] for the iPhone or iPod Touch. I have not played this on my iPod Touch but I had the old click wheel version and found it to be a very addictive and nicely polished experience.