Joint Center for Housing Studies (Harvard University): Center website focuses on housing in the United States, featuring full text of many of JCHS publications.
KnowledgePlex: A "comprehensive interactive resource for the affordable housing and community development field." Registration (free) is required to access some of the material on this web page.
Construction statistics (U.S. Census Bureau) Comprehensive site for U.S. housing construction data.
HUD user--housing data sets (U.S. Dept. of Housing and Urban Development) Terrific site for U.S. housing data and information.