United States and World

• David Rumsey Map Collection.
• Geologic Atlas of the United States. Texas A&M.
• Lovejoy Library Map Collection, with web links
• Lower and Middle Mississippi Valley Engineering Geology Mapping Program. US Army Corps of Engineers.
• National Atlas of the U. S.
• Outline Maps. (free)
• Perry-Castaneda Library Map Collection. University of Texas at Austin.
• USGS topographic maps.
• Geodata.gov. U. S. maps & data

Illinois

• County Coal Map Series. Illinois State Geological Survey.
• Digital Sanborn Maps. Illinois fire insurance maps, 1867-1970
• Federal Township Plats of Illinois (1804-1891). Illinois State Archives.
• Illinois Historical Aerial Photography 1938-1941.
• Historical Maps Online. University of Illinois At Urbana-Chamapaign, University Library.

• Illinois Natural Resources Geospatial Data Clearinghouse. University of Illinois at Urbana-Champaign.
  "A gateway to Illinois GIS data sets and orthoimagery."

Gazetteers

• Collins World Atlas Gazetteer

• Digital Map Indexes. Every index map held in the collection of the Earth Sciences and Map Library at UC Berkeley.
• Index Map Collection. Western Michigan University. Primarily AMS or GSGS map series.
  
• The British Library. Search their Integrated Catalog for "Index to series attached" as a phrase to find all map series having digital index maps (primarily GSGS series (Geographical Section, General Staff)). Choose a set of interest. The scanned index is available from that record.
  
• National Survey Maps, East and Southeast Asia. University of Oregon Map Library.