Portland Buy Local (check out their "Why Buy Local" page for a great explanation of the benefits of supporting local businesses)

Portland Buy Local is a campaign of the Portland Independent Business & Community Alliance. Our mission is to support locally owned, independent businesses in Portland, to maintain our unique community character, provide continuing opportunities for entrepreneurs, build community economic strength, and prevent the displacement of community-based businesses by national and global chains. (from Portland Buy Local)

dsmBuzz (features a great blog on independent businesses)

dsmBUZZ is a grassroots initiative that exists to promote the efforts of locally owned businesses in central Iowa. Our mission is to be a resource for residents and visitors interested in finding out about the uniquely independent businesses in our community. We provide a collective voice for the buy local movement to encourage consumers to support their locally owned entrepreneurial neighbors.  (from dsmBuzz)

Lots more links to come.