This website is <em>free</em> and can give you flash cards with the test questions, filtered by element/chapter. You can start off with just the chapter that you're working on in whichever license manual you choose to go with. It can also give you practice tests, and will keep a log of your progress.
If you want the full deal on the theory, the ARRL books are a great study resource. if you just want to pass the test then the books by Craig Buck are really good at that, they just focus on the test questions with a brief explanation of the question. I've used both for General and Extra