This article is from the Selecting a Dog Breed FAQ, posted to rec.pets.dogs newsgroup. Maintained by Amy Hendrix, with numerous contributions by others.
Go to a dog show in your area. You can't learn everything about a breed when you see it at a show, but it's a good way to get a handle on which breed is which, and a good way to meet local breeders if you've already chosen a breed.
If you can't get to a show, try to meet some adult dogs of your breed in the flesh -- more than one, if you can find them. Do you know someone who has a dog of your new favorite breed? Does a friend of a friend have a dog you can meet? Is there a dog park, dog beach, or dog run in your area where you could meet some dogs and ask lots of questions? Never buy a dog just because you liked its picture in a book.
Get in touch with the national breed clubs ("parent club") for the breeds you like. They will send you information packets on their breed, and they will put you in touch with local clubs and breeders.
Also, find out if there's an all-breed Kennel Club in your area (the AKC can put you in touch) -- it's a good way to meet local breeders and their dogs, and to find out about dog activities going on in your area. Find out if your local club has a breeder referral service -- if they do, the breeders they refer you to will be those who breed according to the club's code of ethics.