When I'm in need of building material for a project at home, I usually have two choices: the hardware store or Craigslist (Habitat's ReStore is unfortunately too far for frequent visits). While I've used Craigslist numerous times (our countertop, cabinet doors, etc) it's nice to have other options for when Craigslist doesn't have exactly what you're after. Meet Diggerslist.
According to the founder, DiggersList was designed specifically to help contractors, property owners and suppliers buy and sell excess construction materials as well as serve as a marketplace for contractors to offer their services. DiggersList is a partner with several non-profits, including Habitat for Humanity LA and Orange County. A few searches in my area yields tons of products for sale in my vicinity. While little of it is what I'd consider bargain prices, it is another resource for DIYers looking for material.
DiggersList is currently only available for 20 states, for specific city's and regions, but there are plans to expand to others at request. Check out your city to see what you can find.
(Image: Flickr member Afroswede licensed for use by Creative Commons)