Library Thing (see the bottom of the sidebar)
While testing LibraryThing, I couldn't help but to see several similarities with GoodReads. I like GoodReads because of the recommendation option and the RSS feed (I receive updates when one of my contacts reviews a book). However, LibraryThink makes it easy to view tags and organize books. I also like seeing the "popularity" of the books.
I hope to use LibraryThing on my school web site to "publicize" new books so students can "see" the covers and even click on them to read a summary. It's proven that seeing the cover image prompts students to check that book out more often. I might try and set that up now...I'll post a link if I get it done.
The image to the right is a screen shot of some of the books I entered that are found on my book shelf at home that I'm looking at right now! :)