Chess is particularly good as it deeply engages both sides of the brain for both novice and expert players as shown in this German study.
Just like an unexercised muscle loses strength, unused brain tissue leads to a loss of brain power. It found that people over the age of 75 who regularly engage in activities like chess are less likely to develop Dementia and Alziemers than their non-board-game-playing peers. Robert Freidland was recently featured in The New England Journal of Medicine. A study of 4,000 Venezuelan students (male & female) showed significant rises in IQ scores after 4 months of Chess instruction.