If you want a new refrigerator, Lowe's does very well. The customer rating system on their web site will steer you in the right direction, you can order on the Internet and get free delivery from a local store, and the prices are good.
For used refrigerators, look around for a used appliance store. You can save money, but the challenge is that they may not last as long.
Lowest cost is probably to keep an eye on local freecycle listings or Craig's List.