Ancient History Sourcebook. Paul Halsall's site at Fordham University. An excellent place to find translated texts.
Latin Library. A terrific place to find Latin texts of most Roman authors. No more typing the Latin texts for tests!
Perseus Digital Library. Has translated and original Greek and Latin texts, dictionaries (including Liddell and Scott and Lewis and Short), and more.
TextKit: Greek and Latin Learning Tools. A site with primary texts in Latin and Greek in .pdf files, Greek and Latin grammars and other materials.
White Trash Scriptorium. A site with hypertext files (requires Windows) of various texts, notes, dictionaries, and commentaries. Also has an interesting place name list.