I've been using Abebooks for a good while now, finding it the best place on the Internet for getting your hands on rare and hard to find books at often reasonable prices. Most often paying more in postage than the cost of the book itself. Abebooks is the Internet equivalent of a dusty-old second-hand book shop.
One thing I wasn't aware of until recently was a secret little corner of the online book store. A place where all the weird and wonderfully surreal books are posted and cherished, by those who love a bizarre title, quirky cover art or a subject that defies reason or understanding.
The Weird Book Room, is a gem of a place to visit. The site blurb itself says that is has been "heralded by the New York Times, Canada's Globe and Mail, The Times of London, and The Guardian (UK) as the finest source of everything that's bizarre, odd and downright weird in books." And even author Neil Gaiman has tweeted about it saying, "Go to this link and gaze on the titles and be made happy. Trust me. It'll work."