LibraryThing
I just signed up for LibraryThing last night. It was exactly what I was looking for. I’ve got a bunch of books on my “to-read” queue and I wanted a way to track them. LibraryThing allows that and so much more. You can add books easily through a bulk upload from your amazon purchase history, share books with friends and see who you’re related to via common books. (Its very much a last.fm for books…)
I’ve added a widget in the sidebar with my “to read” books and here is another version below: