Go to the following link for a list of the different certification agencies.http://www.scuba.com/resources/cert.asp
PADI and NAUI are the two most prolific agencies in North America, but are by no means the only ones. The best way to find a good shop is to talk to at least three different ones and go with the folks that you feel most comfortable with. Look for professionalism and the personality that most fits the way you like to learn something new. There are many different teaching styles and the right one for you will tap you on the shoulder when you find it.