Accessible book catalogs, whatcha got?

[Noisy Rhysling]

A certain lady has over a thousand books right now, with no end in sight. I finally got her to catalog them with Librarything.com. I was amazed when she only had a few dozen duplicates, some of which came from blending our collects. Librarything allows her to check her catalog before buying a book. I've used it for years with no problems.

I am not in any way, other than a user, associated with librarything.com.

To the point: Anybody have a online catalog site they use and like? (Or used and hated?)