nten- tech 4 nonprofits is ur best research star (Score 2, Informative)

http://www.nten.org/ has done reports comparing CMS for nonprofits, including a great comparison of drupal, joomla & plone. Beth's blog, techsoup and netsquared are great resources additionally, you could look into using another serive like donor's resource, firstgiving, givezooks, Mysamaris, and Razoo- most of which have a free option Raiser's Edge, like anything Blackbaud is really great if you can afford it. But I would start at the source of research and read the reviews- they are seriously helpful!