The United States Social Security Administration. How to Get a Copy of Your FBI. The Freedom of Information Act is a powerful thing.
If you've ever wanted to know just what those guvmint bastards have on you, anyway, here's your chance. Just fill in the italics in this form letter with the appropriate information, get your signature notarized, send it off, and you're in business! This should be free, though if your search returns reams of information, you may be charged 5 cents per page in duplication fees.
The law says that your request must be responded to within 10 days, but you can expect something closer to 2 or 3 months for a definitive answer with the current backlog of paperwork. Legal Information Institute at Cornell Law School.