Macrina's ciabatta buns are also good. I can get both their ciabatta and their brioche buns at Metropolitan Market. They may be at other groceries as well.
----- Metropolitan Market 1908 Queen Anne Ave N, Seattle, WA
the poppy-seed kaiser rolls at pike place bakery (near the bronze pig) are just the right size and crunch for burgers - if you prefer a little less texture, three girls bakery across the street has a soft roll more like a commercial burger bun