Here's a list of history-related websites. For additional resources on the web, I recommend looking through the lists compiled by Best of History Web Sites and History Matters.
The historical map collection has over 39,000 maps and images online. The collection focuses on rare 18th and 19th century North American and South American maps and other cartographic materials. Historic maps of the World, Europe, Asia, and Africa are also represented.
Popular collection categories include antique atlas, globe, school geography, maritime chart, state, county, city, pocket, wall & case, children's, and manuscript maps. Search examples are United States map, Geology maps, California map, Afghanistan map, America map, New York City map, Chicago map, and U.S. Civil War maps. Browse map categories: What, Where, Who, When. The collection can be used to study history, genealogy, art, explorations, local and family history.
The accompanying blog contains numerous categories.