Well I guess this is a very regional question, but Powell's City of Books in Portland, Oregon, has a large small press section, as well as having a considerable selection of alternative periodicals in their magazine section (great online presence, too). Elliott Bay Books in Seattle, Laughing Horse in Portland, Hungry Head in Eugene, and Village Books in Bellingham are a few more in the northwest. The situation is far from great, but the reality is that small presses have better access to the marketplace than at any time in recent memory.