This article contained many sources available to GIS users.
Sources are accessible either in text or on the web.
The article cautions that one should take care when using several pieces of data from many sources. It was also interesting to find that most standardized data sources were derived from Federal as opposed to local or state agencies. If one will be working for one of the latter agencies, it seems as though a frustation level exists. That is, dealing with unstandardized data can be cumbersome, time consuming and least cost effective.