If you are doing archaeology within the state of Illinois there are a wide variety of useful resources available on the WEB. If you discover that any of the links are dead, please drop us a note.
USGS Digital Orthophoto Quadrangles for Illinois - The data sets and viewer are free but it takes a little effort to get the MrSID GeoViewer installed and set up. The photographic resolution can be as fine as 1 cm = 39 m.
Eyewitness Accounts of Early American Exploration and Settlement: A Digital Library of Images and Documents
American Journeys - View, search, print, or download more than 150 rare books, original manuscripts, and classic travel narratives from the library and archives of the Wisconsin Historical Society.