The bottom line is that adopting a pet rather than purchasing one saves lives. In fact, you can find your next pet without ever leaving your chair - just visit Petfinder.
We live in a world where very few shelters are "no-kill", which is a true safe haven for abandoned pets. Municipal shelter euthanasia rates are astronomical, and many are measured by the number of animals removed from the streets, not the animals successfully placed in new homes. This means the adoption rates from local shelters is very low, simply because it is not a high priority. Since very few pets get adopted by the public, it is up to local rescue groups to pull the pets from the shelter and find forever homes for them. However, rescues have a finite amount of resources, and many are dedicated to a specific breed, so there are always a number of animals that "cannot" be saved.
If you adopt an animal from a shelter, you have removed that specific animal from death row. If you adopt from a rescue group, you have made room for a death row inmate in the shelter to find a foster home.
The second advantage to adopting is that it begins to slow down the demand for pet store pets. As demand falters, perhaps puppy mills will slow their production. This will take a long time.
It is unfortunate that pets are also products, and that they are relatively easy to produce. As long as there is demand for product, pets will be produced, often times with little concern for quality. However, unlike many products, pets cannot simply sit in a warehouse until needed. They require food and care. Many times, if a purchaser is not found quickly, breeders simply dump their excess product. Once dumped, the local shelter usually gets them, as animal control collects them. Purchasing a pet encourages this cycle. Let's break it.
So, another advantage to adoption is that it could save you money. Less dumped animals means less need for animal services, and that means lower taxes. Eventually.
In the Dallas-Ft. Worth Metroplex, the Metroplex Animal Coalition has a list of local rescues, so you can call the rescue of your choice. Anyone can also use Petfinder to find adoptable pets near them.
Please consider adoption. The life you save will be your best friend's.