Ed Danson’s definitive book “Drawing the Line : How Mason and Dixon Surveyed the Most Famous Border in America” is a must have for those interested in the Mason and Dixon Line.
http://www.amazon.com/Drawing-Line-Surveyed-Famous-America/dp/0471385026

Robert D. Hutton’s documentation of many stones on the line. Bob’s inventory also includes a link to “Topozone” maps showing the location of the stones.
http://www.masondixon-line.com/

In 2002, the National Geographic Channel filmed a news story about the Mason and Dixon Line. This article was subsequently published on their website:
http://news.nationalgeographic.com/news/2002/04/0410_020410_TVmasondixon.html

Scenes and roads from along the western end of the most-famous border in the United States and related locations from southwestern Pennsylvania, western Maryland and northern West Virginia. By Pete Zapadka.
http://www.exploretheline.com/

A brief history of the Mason-Dixon survey line by John Mackenzie, College of Agriculture & Natural Resources University of Delaware
http://www.udel.edu/johnmack/mason_dixon/
 
The David Doyle-National Geodetic Survey Collection of the Mason-Dixon Line Resurvey: Scanned images of the original field notes from the 1901-03 Hodgkins Re-survey of the line. ENTER USER NAME: aaco; PASSWORD: aaco#
http://speccol.mdarchives.state.md.us/msa/speccol/catalog/cfm/dsp_inventory.cfm?speccol=5654&serno=1&a_level=inventory

Wikipedia reference to the Mason and Dixon Line
http://en.wikipedia.org/wiki/Mason%E2%80%93Dixon_Line

Mason-Dixon Historical Park, Greene County, PA
http://www.masondixonpark.com/

Delaware State Boundary Monument Database – contains descriptions and Latitude/Longitude information for the stones on the Delaware & Maryland boundary.
http://www.rdms.udel.edu/dgs/boundaryMap.html

Details from the map of the boundary survey between Maryland and Pennsylvania by Charles Mason and Jeremiah Dixon, 1768. SPECIAL COLLECTIONS (Maryland State Archives Map Collection), MSA SC 1427-74-1/2.
http://www.msa.md.gov/msa/speccol/sc2200/sc2221/000017/000013/html/0000.html

Delaware's State Boundaries, By William S. Schenck
http://www.dgs.udel.edu/publications/infoseries/info6.aspx

Maryland-Pennsylvania Border Disputes – This guide describes maps, manuscripts, and related printed documents useful for the study of how Maryland’s boundaries were established.
http://www.lib.umd.edu/RARE/MarylandCollection/MDResourceGuide/MDPAborder.html

Surveyors Historical Society
http://www.surveyorshistoricalsociety.com/