What it does: Keeps you up to date on the positive and negative payment information on all your credit accounts.

What it costs: Free, once a year, by law. It's also free each time you place a 90-day fraud alert. If you need them more often, $29.95 is the most you should pay.

Should you do it? Yes, at least once a year so you can check for and dispute errors. Items that you don't recognize—such as accounts, judgments, liens, collections, and bankruptcies—might indicate ID theft.

Where to get it: Go to the joint Web site of the three credit bureaus, at www.annualcreditreport.com, where you can order free yearly reports. If you decide to buy more, Equifax and TransUnion charge the lowest prices.

Beware: Some Web sites offer "free" credit reports as enticement for you to sign up for costly credit monitoring. Experian and myFICO.com charge the most for three credit reports—$39.95 and $47.85, respectively. Sellers sometimes charge extra for three credit scores, though they might not be the same ones lenders use to evaluate your credit quality.

This article was also published in Consumer Reports Money Adviser. Subscribe now to get more expert financial advice you can trust.