The FACT Act established the free annual credit report program. Everyone is entitled to a free copy of their credit report once per 12 month period.
Go to
https://www.annualcreditreport.com/cra/index.jsp and fill in the blanks.
Yes, it's legit. Check the FTC website to confirm.
http://www.ftc.gov/bcp/edu/pubs/consumer/credit/cre34.shtm
And this one is not a "watch your credit" site - it's a site set up jointly with the FTC to enable the reporting bureaus to comply with the FACT act.