SPD is the only national distributor dedicated solely to small presses. It's based in Berkeley and its web site affords an airport hangar full--a whole naval base full--of information on the latest work from small presses.
Books of all genres are found here, as well as a list of all publishers who distribute through SPD--if you're looking for small presses, find them here.
Notable New Titles featured on SPD include
Pamela Lu's Ambient Parking Lot, coming in May from Kenning Editions
Michael Stewart's The Hieroglyphics, a "novel(la) in prose poems" out now from Mud Luscious Press
Joel Steven Kuszai's Accidency, forthcoming poetry from Roof Books
Artist Sessions at Studio 35, edited by Robert Goodnough/ Soberscove Press
Kazim Ali's Fasting For Ramadan: Notes on a Spiritual Practice, just released by Tupelo Press