At least, the best one I've had here, and one of the best I've ever had anywhere: the off-the-menu Five Bistro burger at (obviously) Five Bistro: http://www.fivebistro.com

Ground brisket and short ribs, portabella mushroom, gruyere, and a fried egg on top, plus housemade fries, pickle, ketchup, mustard, and aioli!

A thing of beauty, both to look at and eat.