http://www.postcardsmart.com/

http://www.the-dma.org/index.php

http://www.dmnews.com/

http://directmag.com/

http://www.directworks.org/

http://www.nmoa.org/catalog/dma/dma_stats.htm

http://www.nmoa.org/articles/

http://www.listsformarketing.com/201.html