If you know exactly what you want, many retail outlets carry a good variety. You can save money through mail order firms listed in the back of running magazines . If you are a new or injured runner go to a running shop owned by runners. Bring in your old shoes. They will evaluate wear patterns and recommend the correct shoe for you.
Proper fit is important.
Feet swell as the day progresses, so always try on shoes in the late afternoon or evening. Strive for adequate toe room and a snug heel fit. And, no matter how good it looks, don't buy it unless it feels good. There is a tradeoff between cushioning and stability. More of one equals less of the other.