When you find a good, relevant article in a reference source, look at the list of references associated with the article. Usually this list of references will lead you to other useful sources.
Reference books are helpful starting places if you need:
The Barrington atlas of the Greek and Roman World
This important reference work covers the Archaic Greek period through Late Antiquity.
REF Atlas Stand DE29.B32 2000 (See also the 2 volume directory to this atlas on the shelves in the Reference Room: DE29.B32 2000 Index.)
More sites for maps:
Two projects from Stanford University explore ancient Rome in maps:
The Perseus Digital Library provides the full text of classical texts in English, Greek and Latin. The site also has some Arabic texts and some Renaissance materials. In addition, the Art & Archaeology Artifact Browser provides access to images of "a massive library of art objects, sites, and buildings."