I trust tirerack.com after having bought dozens of tires there. Now they have free shipping. They also have recommended install shops where they will ship the tires and give you estimated costs.

On the other hand, local car enthusiasts will always be able to tell you about a hidden gem of a tire shop. I had a big problem with finding people who could reverse- install (tires go on from rear), which typically requires nice equipment. I started off finding someone with a nice car and expensive set of running gear, complimented the car, and ask them where they recommend getting tire work done.