If you received an ebook reader as a gift this holiday season, congratulations! Now you've just got to buy some books so your Kindle, Nook, BeBook or other gizmo is more than a glorified paperweight. Or do you? Fact is, there are hundreds, if not thousands, of free ebooks available. You just need to know where to look. Like everything free, however, there are a few caveats to be aware of.