Remember not to hand over personal information to anyone without first checking them out through a variety of different sources. They aren't all bad, but they aren't all good either. You will need a company with a good reputation.
Look up the name of the company on the Better Business Bureau's website and then pay careful attention to anything that is said about them. The absence of the company name does not mean it is reputable. They may be new or it could be that nobody has taken it upon themselves to report them. Talk to other people who have used the company if you can find them. There are sites online set up specifically for complaints concerning this type of business.
A good debt consolidation company will not ask for higher interest rates than those you are already paying and they won't ask for large amounts of money in fees in order to "process" your loan. The best debt consolidation companies have a decent working relationship with most creditors and will provide credit counseling for you as part of the service they provide. You should have your questions answered without being put off or charged for time.
If you want the best deal from the most reputable place, find a good non-profit debt consolidation company. While they aren't charitable organizations, they are low cost and usually effective at negotiating with your creditors and getting your interest rates lowered. They may even be able to get an account settled for a lower price than owed. Research non-profits in the same manner as any other company. Some claim to be there for you when the truth is, they are there for themselves.
A good place to look for advice and information is the National Foundation for Credit Counseling. The NFCC gives accreditation to debt consolidation services based on a set of guidelines that are ethically sound. They may be able to direct you to a reputable debt consolidation company in your area.