One of the more interesting things that you can now do is request a free copy of your credit report each year. I'm not talking about one of those ads that require you to sign up for something to get it free - Congress passed a bill that requires this. All members of the country can get one for free from each credit bureau each year.
It was always interesting to me to see what information showed up there. Another thing that I found when I first got my free one was that I had credit cards open that I didn't even know about (probably due to those free t-shirt offers or something).
Knowledge is power, and this site gives you access to what people who will lend you money will see when they decide how cheap of an interest rate to give you on a car loan or house loan.
annualcreditreport.com
