There are a lot of great sites on the Internet for history geeks like myself and more and more are coming on-line every day. The following are a few suggestions. I hope to add more in coming months.
General Reference Sites
University of North Texas Digital Library. Particularly useful for its very large collection of digitized U.S. Government reports, such as Farmers’ Bulletins. http://digital.library.unt.edu
The Library of Congress. A grand collection of digital materials including historic maps, photographs, manuscripts, HABS/HAER recordations, and historic newspapers. www.loc.gov.
Internet Archives. A lesser known, but in some ways, more useful collection than Google Books. Has a lot of full-text downloadable sources on various aspects of history. www.archives.org.
The National Archives. The National Archives is digitizing increasing amounts of primary source records which they are putting on their sometimes a bit difficult to negotiate website. www.archives.gov.
The Making of America. Paired websites operated by Cornell University http://cdl.library.cornell.edu/moa) and the University of Michigan (http://moa.umdl.umich.edu) that contain full-text articles from nineteenth and early twentieth century humanities and scientific sources.
United States Geological Survey. It used to be that to get a topo map one had to trek down to the nearest camping store pay eight dollars, and then come back to your office and mar the map with a series of inaccurately drawn lines in an attempt to figure out map locations (UTMs). That is no longer necessary due to 1) the advent of portable GPS receivers and 2) the creation of software to easily determine UTMs on-line. The USGS was responsible for much of this evolution, and its website is wonderful, including downloadable and geo-referenced copies of both current and historic topo maps (all for free–your tax dollars at work). www.usgs.gov
New York Public Library Digital Gallery. A huge collection of historic digital images whose geographic breadth extends well beyond the border of the city and state. www.digitalgallery.nypl.org
Historic Agricultural Websites
National Agricultural Library Digital Collections. Treasures from the U.S. government agricultural library in Greenbelt, Maryland. http://naldc.nal.usda.gov.
Cornell University Core Historical Literature of Agriculture. An extensive collection of digitized publications from Cornell’s incomparable Mann Library. http://chla.library.cornell.edu