Open Library is an interesting site that has been around for a couple years now. It is an online catalog whose goal is to have a page with a record and description for every book ever published. So in a way it is a little like WorldCat, which we have provided access to for years. WorldCat is probably more accurate and in depth for "bibliographic" details, you know, those things librarians love, lol, like which edition is it, what library owns it. But for some books Open Library provides narrative description of what the book is about, something WorldCat doesn't do, and if you are interested you can add information to Open Library, help build it up.
Open Library is also a venture into e-books, with a small library of e-books of it's own you can "borrow," and links to other libraries whose e-books you may be eligible to use. Click here for more info on it's e-books.