There used to be a book review forum called The Wall (can't seem to locate it anymore) in which folks posted books that deserved to be thrown against the wall. I know that I added a few to the listings there.
One book that will forever stick in my brain as one of the worst books is Laurell K. Hamilton's "Incubus Dreams". That's the book in which she self-destroyed her Anita Blake series, IMO.
Another is Talia Gryphon's (should have known right from the author's name) "Key to Conflict". That was just so poorly written and edited, it didn't deserve to be published. For a hint, see
http://satireknight.wikispaces.com/Talia+Gryphon