Go to CharityScorecard.org.
In 2006 the OpenAgenda.org web site was replaced by the newer CharityScorecard.org site. I've left the old OpenAgenda.org content here just for the historical record.
I'm just getting started on this page, so there's not much here yet. Hopefully in time it will grow to be small "database" of information about non-profit organizations that seem like good candidates to look at more closely.