Many historical maps of Maine are available online. The following sites have online collections:
United States Census Bureau State and County Map. This map will allow you to zoom in on any state or county in the United States and read the names of all of the neighboring counties.
The University of Maine in Orono, the Maine Historical Society, and Bowdoin College in Brunswick have large collections of maps and atlases. The Bangor Public Library is also a good source of maps.
The Family History Library has a few individual maps of Maine. These often show the locations of towns, rivers, roads, townships, and county boundaries. A few of the Maine maps in the Family History Library's collection are:
Carleton, Osgood. A Map of the District of Maine. N.p., N.d. Reprint. Originally published 1793. (FHLmap case 974.1 E7c). This also includes a map containing the location of areas with the most Indian problems.
Greenleaf, Moses. Map Exhibiting the Principal Original Grants and Sales of Lands in the State of Maine. Ellsworth, Maine: Ellsworth American, 1977. (Family History Library map case 974.1 E7g).
Maine County Subdivisions, Towns, Plantations, Unorganized Territories, and Places. Washington, D.C.: U.S. Government Printing Office, 1977. (Family History Library map case 974.1 E7mc).
For individual locality map information, see the Place Search of the Family History Library Catalog under MAINE, [COUNTY], [TOWN] - MAPS.
Printable maps are also available from the National Atlas of the United States -- http://nationalatlas.gov/printable.html