Most (though not all) credit repair companies are basically big pyramid scams and are not effective. If you are organized you can do it yourself. There are books out there (go to a bookstore and take a look at the offerings) and also sites on the internet which explain how to do credit repair yourself with sample letters etc.
I work for Bank of America Home Loans and we have a service known as "rapid rescore" which has helped some of my clients raise their credit scores dramatically. However, this only works in certain instances. Fo instance, if you have had legitimate late payments your score will not change. However, there are other circumstances which could lower your score and are very fixable
If you would like, I can take a look at your credit for free and let you know, in my pinion, where you stand and recommend some books.
Bank of America Home Loans
201 741 5269