Entertaining Your Brain?

Spencer Wilson asks: "I'm constantly told that I have an extremely high intelligence. I always feel like I should know so much more, though. Do you, the Slashdot readers, know of any ways to improve ones brain power? Perhaps books, Web sites, etc., that provide questions that involve ways to increase memory, creativity, mental agility, logic reasoning, intelligence, etc. Are there any diets/exercises that really help?"