Just saying

[Cain]

http://manybooks.net/
http://bookcrossing.com/
http://libraryelf.com/
http://www.scribd.com/
http://worldlibrary.net/
http://www.freetechbooks.com/
http://www.bookins.com/
http://welltoldtales.com/
http://www.wowio.com/
http://www.bizbooktalk.com/
http://www.chmpdf.com/archives/ebooks/
http://www.titletrader.com/
http://www.zunafish.com/
http://www.baen.com/library/
http://www.librarything.com/
http://www.podiobooks.com/
http://www.bookrags.com/browse/ebooks/
http://www.bookyards.com/
http://www.docstoc.com/
http://librivox.org/
http://en.wikibooks.org/
http://www.dailylit.com/

Any of these may be of interest.

[Triple Zero]

randomly clicked "library thing", seems like a community of people cataloging their book collections, adding tags and reviews. could be useful for figuring out what a book is about before reading it.

[Kai]

This is an awesome list to add to Avaxhome, gigapedia and bookchan.

Edit: in the sense of more reading resources.