I am impressed with Cramberry, a free online source for flash cards. You create a free account. From there you can either create your own deck of flash cards or browse decks that others have created. When you find one you like, you simply “add to your set.”

The thing I like about this site is that there is no multiple choice involved. You are presented with the question and have to come up with the answer out of your head. When you click the mouse, you see the correct answer and rate yourself as being correct or incorrect. Incorrect answers cause that question to be recycled so that you get another chance at it later.

This one is definitely worth a look.