Run, don't walk, to Mamma's in Edinburgh. It's an American-style pizzaria that offers a gluten-free crust, plus other gluten-free entrees, desserts, and beer alongside all the "regular" food. It was delicious. It was just like regular pizza. And it was such a mental pick-me-up, to be able to sit down and order pizza and beer just like everyone else.
We went to the Grassmarket location. The website says it's take-out, but they had a sit-down restaurant. You can see their full menu online. Most of the toppings are gluten-free as well, but I didn't want anything fancy. Just plain cheese and pepperoni for me. Mike had a bite and thought it was comparable to his crust. He said neither pizza lived up to his New York standards, but both were superior to the pizza slop they serve in California.
(Clicking on the image will take you to vacation pics on flickr.)