LibraryThing is a useful tool to catalogue all your own books onto a website.
This is one of these brilliant ideas that looks neat but only really comes through once you actually try it. Because it links all your own books to those of other users. And their ideas and thoughts. And because the whole thing is based around "tags", you can quickly follow up everything that interests you and see what like-minded people are reading and where their interests took them. This has much of the appeal of del.icio.us, but as applied to the printed word (and, let's face it, the printed word isn't history yet...)
But it gets better - because the site now offers a very smart "Talk" feature which uses tagging/linking from within comments (in a similar manner to Wikipedia) and then aggregates these links against your own Library so that all the comments made about a particular book or author appear in context - even if those comments were made on another page and by another user. I guess this works in a similar manner to the "Lists" that Amazon displays, but at a more granular level - and with a more contextual presentation.
Find more here: Introducing LibraryThing's new Talk feature.