The Internal Revenue Service
Downloadable tax forms and publications as well as a lot of great tax advice.
Social Security Administration
Learn how the Social Security Administration can help with your retirement, medicare, disability, survivorship and other benefit questions.
U.S. Small Business Administration
You don't need an MBA to use the SBA. This site outlines everything in plain English. The SBA site contains a wealth of information for entrepreneurs and small business owners.
U.S. Department of Commerce
A thorough overview of the Commerce Department and the organizations under its banner