Ever wanted to catalog the books you own, but didn't have the wherewithal? Check out LibraryThing. What is LibraryThing? According to the web site: "Enter what you're reading or your whole library—it's an easy, library-quality catalog. LibraryThing also connects you with people who read the same things." You can enter 200 books for free, or as many as you like for either $10 per year or $25 for life. One thing that makes this nice: you can search for, pull up and click on many common books, making it unnecessary to enter the information manually.
Thanks to Kevin Higgins for mentioning this on his blog, which is where I first heard about it.