Serious Bread: Vital Vittles Sourdough Rye
Their flagship Real Bread is a simple, dense, yeast-raised, 100% whole-wheat loaf that makes great toast. Most of the bakery's other breads are minor variations on that, with seeds, nuts, other grains, raisins, or corn mixed in. To me, all those breads taste pretty much alike, though the millet in the sesame-millet loaf adds a distinctive and pleasant crunch.
One exception to the taste-alike rule is the Russian Sourdough, an even denser bread made from nothing but whole-wheat flour, salt, water, and whatever wild bacteria and/or yeast ferment the dough. I prefer the Sourdough Rye, a very similar bread made with a percentage of rye flour and some caraway seeds. Sliced thin, this makes great German- or Scandinavian-style open-faced sandwiches.
You can find Vital Vittles' breads all over the area--there's a list of retailers on their Web site. They also sell at farmers' markets in Berkeley, Oakland, and Pleasanton, and at the bakery (2810 San Pablo, Berkeley).