I created this list a couple of weeks ago and I thought that it might interest some people here. It's still not complete, but there are enough resources there to keep you reading for quite a while.

Great list! Another good one -- check out LibraryThing, which is my personal favorite.

I have used LibraryThing in the past and have enjoyed it. I will add it to the list when I get around to creating a section for sites that allow users to catalogue their collections.