An on-going list of vendors for re-used materials...many of these places accept re-used materials as well as sell/distribute them.

Building REsources, San Francisco:
http://www.buildingresources.org/index.html
Description from their site: "San Francisco's only source for reusable, recycled and remanufactured building and landscaping materials. Building Resources is a not for profit organization dedicated to providing our community with low cost high quality materials, in a friendly, clean and organized setting. Our 1 1/2 acres are full of wonderful finds and great values. Project ideas are demonstrated throughout our buildings and gardens, all of which are built using 100% reused materials."

The ReUse People, nationwide (with Bay area locations in Oakland and Sacramento):
http://thereusepeople.org/
Description from their site: "We are a nonprofit, 501(c)3, corporation dedicated to keeping usable building materials out of our landfills and providing them for reuse. To date we have salvaged hundreds of thousands of tons of usable building materials."