Creditkarma.com is powered by TransUnion. After putting in your personal information, you will get your TransUnion credit score. Not only will you get to see your credit score but it will allow you to see how much debt you have and which areas you need to improve more. It also allow you to calculate what your credit score may look like if you were to make changes to your credit such as opening a new credit card or a loan.
Creditsesame.com is powered by Experian. It is similiar to creditkarma.com but it has a bit more features. It allows you to manage your debt, if you own a house, it will also estimate the value of your home. You can also set your goals, get advice on which credit cards can save you most money and much more.
They are both great sites and can't go wrong with free credit score! Of course these sites won't go into all the details like how much you owe on which account (you'd have to buy a credit report for that) but I still love the fact that I can keep track of my credit score for free.
Do you know any other free credit score sites?