The National Alliance to End Homelessness is an overarching organization in the U.S. that covers all agencies working with people experiencing homelessness.  They have a very active blog at blog.endhomelessness.org, and I had the privilege of having a guest post on the site.  In the post, I talked about the importance of all people who are working to address homelessness to also include looking at public policies.  You can read the full post at: http://blog.endhomelessness.org/?p=2778.