The first step in determining what type of dog you want, is deciding if you want a mutt (mixed-breed) or a purebred. A mixed breed is a domesticated animal descended from multiple breeds of the same species whereas purebred denotes a pure strain obtained through many generations of controlled breeding for desirable traits. (Definitions from http://www.thefreedictionary.com)
If you are not looking for your dog to serve a specific purpose aside from being a loving, loyal, companion a mutt would be your best bet. They are generally easy to find, inexpensive, and are every bit as loveable as a purebred. Humane Societies and Animal Shelters are always my first choice when searching for a mixed breed. You can take an in depth look at both types of facilities by clicking on the Adoption tab at the top.
If you are looking for a dog with certain physical characteristics, or to serve a specific purpose, i.e. hunting, racing, showing, breeding etc. you may want to look into purchasing a purebred.
Even when looking for a purebred dog, I would always suggest visiting nearby animal shelters first. You may find exactly what you are looking for. If not, here are some other options.
I recommend finding a purebred through a Rescue Organization. Rescue Organizations are privately owned and dedicate their time and resources to one breed. I purchased a Black Labrador Retriever from a Rescue Organization out of Salt Lake City. It was exciting to add another member to the family, and also rewarding knowing we were giving him a chance at a better life. I prefer to search online for local Rescue Organizations at either http://www.petfinder.com or http://www.adoptapet.org
Looking for a registered Purebred? Purchasing a registered purebred ensures there has been no break in the lineage and provides documentation of the dog’s ancestry. If you are looking to invest more than two or three hundred dollars, the best guide to selecting a registered purebred is through the AKC (American Kennel Club). I recommend you visit http://www.akc.org to learn what different types of registration there are, and also to obtain contact information for local breeders.
If you aren’t sure what type of purebred you are looking for, the AKC website also includes a guide to help you determine which breed(s) is right for you.