This month's Wired has more on the exercise/cognitive function connection : aerobic exercise helps, weight lifting doesn't.

They also have a rundown on drugs that allegedly enhance cognitive functioning, handy for any who are thinking about emulating the 20% of scientists admitting to using brain-boosting drugs in a recent, informal survey in Nature.

The drugs have questionable efficacy, are expensive, and have nasty side effects (which Wired details - my favorite, for methamphetamines: "Prison"). Exercise, in contrast, works well, is free, and is beneficial pretty much all around. Forget the drugs - put on some sneakers and go run.