Great overview of all sorts of topics, has all sorts of quizzes etc. Great source and general financial reference wiki.
Investopedia taught me almost everything I know about finance. It's a great place to start. Also, and I know I'll get reamed for this, if you want to learn the basics of stock trading, check out some of Jim Cramer's books. His books do a good job of breaking down the stock market into lay man's terms. I know he's a pretty polarizing figure, but the books are a good introduction to fundamental analysis.