My neighbors, who spent the last 2-3 years teaching in Japan, introduced me to this site. They have online tutorials and games based on some 15 years of research into the most efficient ways to acquire knowledge. http://smart.fm/about/learning_science talks about their research; noteworthy is the "Ebbinghaus forgetting curve," which basically shows that the best way to remember something is to remember it just before you're about to forget it.
Check out their "BrainSpeed" game. Much more fun than flash cards.