The Martin Gardner books Aha! and Gotcha! have great re-readability as you age. The comics can easily be read by kids and the text as they get older. Man, I LOVED those books... I think I first dipped into them in third or fourth grade and brought them with me to college, working out the harder problems as I got more skilled in proofs. Also good is Math for Smarty Pants, though it's at a lower level and doesn't have the re-readability. They're recreational math and lots of fun. I sure wish I could get Square One TV on dvd (you can watch on youtube, but it's not great quality).
