This project *screams* wiki to me....

What about Ebsco's NoveList? I guess it's not very 2.0, but neither is OCLC's Fiction Finder. NoveList is freely available online to many people who have a public library card. Disclosure: I write freelance articles for NoveList, so I'm not an entirely disinterested party, but I really do think it's better than a lot of the ones you've listed above. I'd be interested to see other people's thoughts on NoveList vs. these free services.

What about www.bookmooch.com. Its very new and lacks the books, but it'll reach a tipping point soon.

Libraries with marvelous-to-me readers advisory programs include the

St. Joseph County Public Library http://www.libraryforlife.org/subjectguides/index.php/Main_Page

and the Waterboro Library (Maine) http://www.waterborolibrary.org/bklista.htm

Again, these materials were formulated before the 2.0 phenomenon, but we use them all the time.

http://www.whatshouldireadnext.com is also useful.

And _What Do I Read Next_, from Gale, complements NoveList.

Great list! I hope you don't mind if I try incorporating some of them into my Rollyo Readalike test site...

God help us! Wiki formatting is the death of anything serious -- the triumph of free time over serious or truly informed.

I found Springfield City Library's guide by accident (http://www.springfieldlibrary.org/reading/booklist.html) and it seems remarkably comprehensive although it is a series of static pages not a database...

This is a bit of a self-promotion, since I work with BookLamp, but BookLamp.org is a new-comer that analyzes the full-text of a book for stylistic trends, and finds matching books based on the results. Very much like Pandora.com, but for books (that's the quickest way to describe it).

Anyway, it's worth at least checking out, I think:
http://booklamp.org

www.shelfari.com
and
www.bookrabbit.com
are great ones.