I discovered 800 Degrees after a few stays at SLS (it is tucked away, far from the entrance) and now it is my "go to" restaurant whenever I'm in Vegas. The crust is divine and all the ingredients are fresh and tasty. Try the Margherita with yummy basil.
Oh, and unlike the $70 pizza rumored to be sold at Rock in Rio USA, this place right across the street is around $10 - $15, depending on your toppings. WELL WORTH THE SHORT WALK!
Best of all, the staff is super kind and interactive with the customers.