PolicyMap is a collection of more than 4,000 data sets that can be overlayed on top of maps. Users simply pick what data they want to see from drop-down menus, and they show up instantly.
It can locate superfund sites; show you crime stats; tell you about mortgage originations (including things like subprime mortgages to various demographic groups), and age and educational background. The data is at a variety of resolutions (some are per ZIP code, some by census tract) and timeliness (census data, for instance, is only current up to 2000).
PolicyMap is free to use for public data. Some data sets, such as home sale statistics, require a paid membership, which costs $200 a month.