I think almost as long as I've been a programmer I've tried making little games to test my reflexes and challenge my memory and other cognitive faculties. It's just been a given to me that: (a) you can train your brain in a manner similar to lifting weights or jogging and (b) this is a highly desirable goal.
The problem is that I've never really had enough faith in the games that I created that the effort I put into them (both writing and training with them) would be worth it. Doesn't stop me from getting interested in the idea anew every once in a while. And it seems that there is a general growing interest in these types of games, growing research that they work and (best of all) an increasing number of open source games that are created specifically to help you train your brain.
Of these sorts of games and research results it *seems* that the one with the most credibility is the "n-back task" as described in this wired article and as implemented in Brain Workshop.
Besides the research, one of the things that gives this game credibility is that it is really challenging and not very game like. It really does feel like exercise (in the sense of forcing yourself to go to the gym because you know it is good for you, a necessary evil). And honestly the first few passes through are almost laughably hard. You are trying to maintain a memory of positions and letter values being thrown out you and notice if the position or letter value is the same as n turns ago.
And the funny thing is that even after a couple of days of not really spending too much time on it, I'm definitely getting better at it. It's actually a weird feeling. The first few times through is just chaos and then all of a sudden you start moving from a slight guess that, yes, I think they did say "C" 2 turns ago and are now repeating it, to being really confident. But of course as soon as you get good at 2-back, it graduates you to 3-back.
Now the problem is how do I test if I am indeed getting smarter? I'll let you know if my brain seems like it has kicked it up a notch or two.