Tufts University: Perseus Digital Library.
Massachussetts Institute of Technology: Internet Classics Archive.
Loebolus: PDF texts of public domain Loeb editions.
Latin for Everyone! Loebulus! (And who will pay Plutarch?) Links to more sources for public domain Loebs.
Livius.org: Articles on ancient history.
Perry-Castañeda Library Map Collection: Maps from Dr. Butler's Atlas of Ancient Geography by Samuel Butler, London: Longman, Brown, Green, and Longmans, 1851.
Ancient World Mapping Center: Free maps.