All of a sudden there are a couple more on my (local to Phoenix) radar:
Smashburger (I ate at the one on 20th and Camelback)
Blu Burger Grill (101 and Northern)
Blu Burger being the better of the two. Better than most, really. They have Angus, Kobe and Bison to choose from. Lots of variation possibilities. I liked it better than Cheeburger Cheeburger by a wide margin.
Smashburger is recommended too; but not as enthusiatically as Blu.