The Berrymans have a song called Homeless..

there is a radio show http://news.homelessnessmarathon.org/
that airs each winter that focusses on the homeless

I have a recording of christmas songs done by homeless people
(not sure of the title or record company)

here are some links:

this one from Nashville looks most interesting...
http://www.amazon.com/HOMELESS-AMERICA-Twenty-One-Conscience-Century/dp/B000BGQSZE

http://www.songfacts.com/category-songs_about_homelessness_or_desperation.php

http://answers.yahoo.com/question/index?qid=20070831170952AAh73m0