Library Thing might be my favorite site on the Internet.
I record everything I read as I read it, and rate it, even if it's so bad I don't finish it, hopefully this helps me not to be attracted to the same book again. I review only occasionally mostly books that don't have any or not a lot of reviews and try to balance good and bad comments. Collections are part of the entry, some basic and some member created, I track books I own, books from CPL, books I want (mostly paperbacks in a series) and books I read years ago and don't own. Tags most users use for subjects, I tag things I will want again for programs, this replaces the wish list that one could keep on the CPL site.
LT has lists of series and charactors which is handy. There is a forum for asking help finding books from whatever details one remembers, one for knitters, and one for librarians.