How many times has it happened? You read about a stock in a newspaper or wherever. And you think, "Hey -- maybe it's worth a buy." What stops you is the thought of doing all that research -- the kind of due diligence investors should always do before buying a stock. If you're that kind of careful investor, here's some good news: Visit a dozen or so key Web sites and you can perform due diligence on a stock in just a few hours. Seriously. All the tools and research on these Web sites are free. Obviously, you still won't be on the same level as the professional analysts who watch the stock day in and day out. But trust me, you'll have it all over investors who dive into stocks without looking. And that little bit of extra knowledge can go a long way.