The Bureau of Labor Statistics is part of the US Department of Labor and collects information about employment and industries. The website is not modern, but the data is top-notch. Be sure to check the tab for "data tools" or "publications."
American FactFinder is a project of the US Census. Just search a zip code or town to see detailed information about that community!
The Census Explorer database includes interactive maps on household income, education levels, employment patterns and more down the census track level (much smaller than county level). This website uses Flash and works best in Firefox, not Chrome. You may need to click "allow" to activate Flash.
DataUSA is an industry / academic partnership to make important data available and accessible to the general public. They draw from 17 separate agencies, research institutes, and non-governmental organizations to make maps and visualizations comparing datasets. NOTE: there is a LOT of information here and the visualizations are amazing, but it can be overwhelming. Be careful to stay focused on the question you are researching!