Dover Books A good, cheap publisher. Like all publishers, the quality varies, but everything is nicely bound. Things I like from them: "Counterexamples in Topology", "Counterexamples in Analysis", "Mozart: Complete Sonatas and Fantasies for Solo Piano"
Powell's Books Pricey, but a wide selection.
Alibris A marketplace for smaller shops; I have purchased a book through them; the service was reasonable.
FetchBook.info A search engine for other bookstores.
World Retail Store
Copyright 2005, Daniel Herring