The George Mason University Homepage is building a substantial Latin Library in HTML format. Latin texts and fragments are also available at Urich Harsch's beautifully presented Bibliotheca Augustana . The Online Books Page and The Great Books Homepage also provide many links worth following up. The best source for classics bibliography is now the Gnomon bibliographische Datenbank. TOCS-IN is still worth a try.
Many bookshops are now online.
Com Books has a very large inventory, offers good prices, and is fast. Blackwell's Classics List is worth a browse. For books on archaeology, Archaeology on the Net is also worth a look. Aesop via gopher from the ccat server at Penn. Summary of Apollodorus' Library from the Perseus Project.