Books at Sixpence - Antiquarian, out of print books and ephemera for sale by mail order only, no credit cards. Comprehensive free use of wants pages. - http://www.booksatsixpence.co.uk/
Bookfayre - Database of Collectable Books, Magazines and Comics on sale from UK book sellers. Many other useful resources for book enthusiasts. - http://www.bookfayre.co.uk