AnnualCreditReport.com is free, mandated by law to provide you with one report from each of the big three credit bureaus once every 12 months. Note that you don’t get your FICO score (aka your I Love Debt score), just the reports.
FreeCreditReport.com is a business, selling worthless credit monitoring and tossing a free credit report in the deal.
Rule of thumb: Don’t trust any website with the word “free” in its domain name with your credit information.
Some detail about annualcreditreport.com: Wikipedia