About Census Tracts (using North Carolina as an example)
UNC Library
http://www.lib.unc.edu/reference/govinfo/census/smallhist.html

City Planning Commission
http://planning.city.cleveland.oh.us/census/factsheets/cpc.html

NEO CAN DO (at CWRU)
http://neocando.case.edu/cando/quickProfile/interface.jsp

NODIS
http://nodisnet1.urban.csuohio.edu/nodis/90census.shtml