Idealist.org is an excellent website for people looking to work in non-profit and social work positions. I have used this site for my own job search, and have gotten several interviews. He is the links, and be aware it is updated regularly:
http://www.idealist.org/if/idealist...gs=modificationDate&validStatusTypes=APPROVED
http://www.idealist.org/if/idealist...gs=modificationDate&validStatusTypes=APPROVED