American Ethnic Geography: Maps Related to Politics in the United States addresses issues of political regions, death penalty and executions and voter participation.
David Rumsey Map Collection is large collection of historical maps.
ESRI Map Book Gallery has online copies of the ESRI collection of Map Books, which contain specially selected thematic maps submitted by people from many different disciplines.
Maplecroft Maps gives users the ability to create global maps with a wide variety of variables, including environmental, economic, political, and social issues. Free registration is required.
National Atlas has pre-formed maps as well as a Map Maker with hundreds of layers on different subject areas to make customizable maps of the U.S.
National Geographic MapMachine includes historical maps along with much other thematic maps.
Perry-Castañeda Library Map Collection Historical Map Sites is the University of Texas' extensive list of links to historical map sites as well as individual maps, covering the U.S. and many world nations.
Same-Sex Marriages (SSM) & Civil unions from Religious Tolerance.org has maps about U.S. statewise marriage laws, relationship recognition, anti-discrimination and hate crime laws, adoption and education laws.
Stem Cell Policy: World Stem Cell Map color codes the flexibility of stem cell research policy in countries throughout the world, with genome sequencing centers also indicated.