I sent $10 to Tim Spalding at Library Thing because I'm a sucker for his website. So far, I've cataloged about half my personal library , and after another 100 titles or so I'll have to start looking in boxes to put up more because I forget the stuff I packed away years ago. You can start your own list at Library Thing for free, but there's a cap of 200 titles.
My favorite feature is the Blog Widget, which generates a display of random titles (on the right of the page about a third of the way down). Somebody clicked through a title to Amazon last week and bought a bunch of stuff--thanks. In two years I've made several hundred dollars in GCs that way! Library Thing also lets you categorize, review, and otherwise manipulate your books, and it also automatically does recommendations based on the libraries of those who have your books. Cool stuff!
I also really, really like our new Verizon DSL hookup. Half the price of Earthlink and Earthlink DSL didn't work on our line (I wonder if that's because Verizon scrambled them somehow?).