Excellent Source for Historic Census Data and GIS Files

I am currently working on a project for The Trust for Public Land in the North Coast of Oregon, part of which involves an analysis of development patterns and trends. In working up numbers for population and housing units, I came upon an excellent source for historic U.S. Census data, the National Historical Geographic Information System. They provide access to the complete Census database for all of the decennial censuses back to 1970, as well as geographic boundary files for mapping the data. So far it has proven to be quite a goldmine!