Glutenfreeda.com put together an awesome list of gluten-free pizzas, pre-made doughs, and mixes. Here is a round-up of their suggestions.
Tom Sawyer Gluten-Free Products: GF flour
Still Riding Pizza: Frozen GF pizza crusts
Gluten-Free Naturals: GF mixes including bread mix, muffin mix, cake mix, pizza crust mix, brownie mix, cookie mix, and pancake mix
Better Batter: GF flour
Rustic Crust Pizza: GF Frozen Pizza
Pamela's: GF bread-mix (for pizzas) and many additional GF products
Tastefully Gluten-Free: GF pizza crust mix, and other mixes including chocolate chip cookies, sugar cookies, bread and roll mix, chocolate cake, all-purpose cookies, and brownie mix
Bob's Red Mill: GF mixes and tons of other gluten-free products
Namaste Foods: GF pizza mix and other gluten-free products
Amy's Kitchen: Frozen GF pizzas including rice crust, rice crust spinach, and non-dairy rice crust (Amy's had always been my favorite pizza but I always found myself eating a whole pie in one serving. Lately, heir prices have been outrageously high at Fairway so I haven't been buying them. It also keeps me from eating a whole pizza in one serving.)
Orgran: GF pizza and pastry multimix and many other gluten-free products
Dad's Gluten-Free Pizza Crust: GF pizza crust
Glutino: various GF pizzas (Currently my pizza crust of choice!