Stumbled across the eHistory project today. It has an interactive map of the Invasion of America which is described as:
Between 1776 and 1887, the United States seized over 1.5 billion acres from America's indigenous people by treaty and executive order. The Invasion of America shows how by mapping every treaty and executive order during that period. It also contains present-day federal Indian reservations.
The interactive map and exploration of the various treaties and orders is fascinating.
They have a number of other projects, including a visualization of the spread of smallpox across North America. Most of the team is at the University of Georgia and some of the projects are less than fully-fledged, but they're all interesting.