The Library Thing must be every geek's dream widget. With it, you can catalogue your books online. So far, I've uploaded nearly a hundred of my books. Mostly, these books are the ones piled beside my desk and perhaps read in the last couple of years.
Check out the meager contents of my library here. Or you can just check out the sidebar for random book covers.
Bah, I'm sleepy and there's a wall full of books to go.