search across all the following databases:
Data and documentation
Common questions and answers.
Entire collection of data resources.
American FactFinder is the Census Bureau's portal for access to tabular data. It includes data from the Census, American Community Survey, and Population Estimates. Currently, there are two interfaces. The older interface will be discontinued by 2012.
Social Explorer provides a very intuitive interface to tabular census data from 1790+, including data from the ACS. It has original tables as well as pre-made reports, which are similar to the Census Bureau's subject tables. The main downside to this site is that it does not report margins of error. This can be an issue for the ACS.
Another caveat is that the premium content to Social Explorer requires a subscription. UM subscribes to this, but if working from home, you will need to make sure you go through a UM portal to get access to it.
National Historical Geographic Information System [NHGIS]
This is the source for the majority of the data in Social Explorer - based on data from the US Census Bureau. However, I would recommend Social Explorer as it has a more intuitive interface. Currently, NHGIS is modifying its interface. The jury is still out on that.
Currently, NHGIS also does not include data from the ACS. On the good side, NHGIS provides shapefiles for historical years, e.g. before TIGER existed.