Comparison of Drupal, Plone and Joomla

Idealware.org has a good comparison of Drupal, Plone, and Joomla, from the perspective of non-profit organizations:

http://www.idealware.org/articles/joomla_drupal_plone.php

"So which tool do we recommend? That depends on your circumstances. Are you going to install and configure the tool yourself, or are you going to hire a web developer to do it for you? What’s your budget for setup and ongoing hosting? In general there’s a tradeoff: do you want something that is less expensive and more focused on getting a basic site up quickly, or do you want something that focuses more on powerful features, stability and extensibility?

For simpler requirements or lower budgets, Joomla, or possibly Drupal, should suit your needs. If you need something powerful and proven, and are willing to commit the resources to make it happen, Plone is likely to meet your needs, but Drupal is also worth a look. Do you want tool that serves groups that are somewhere in the middle, that need a straightforward setup but also a fair amount of power? That’s where Drupal excels. Of course, this may change over time. Joomla is getting more powerful (and, as our examples show, it is already serving large, highly visible organizations), Plone is learning from Drupal and Joomla, and Drupal is getting both easier to use and more powerful with each release."

I use Drupal for most of my sites, but I may check out the newest version of Plone (3.0) soon.