I am trying to organize a tour of sorts, in search of the best gourmet burger. Under "gourmet burger" I do not include e.g. Barney's. While they have a nice variety of toppings, the quality of the burgers themselves, and many of the toppings, is not particularly high. So far, my favorite burger is at ZAX tavern on Telegraph in Berkeley, and I'm planning to try Cafe Rouge's as well. I'm wondering what other places have a great gourmet burger, especially here in the east bay.