University of Michigan's Historical Census Guide
Excellent overview of various historical census materials.
NC State University Census Guide
Guide to Geolytics Census CDs - CDs are located in the Scholars Lab.
The Census CD+Maps series, produced by GeoLytics Inc., provides easy access to US census data from the past several decades. Data cover the entire nation and can be viewed in tabular form, downloaded in many formats, or mapped in GIS-compatible files. Information from the CensusCDs are not online, and the CDs must be used in the Scholars' Lab. However, you can download information and store the files electronically for later use.
The CensusCD Neighborhood Change Database (NCDB) is especially useful to tract demographic change in a small geographic area.