Hey Lisa,
Great question as I have been doing research on this myself. I'm getting ready to start yet another site and plan to test out some different CMS's so I can review them on my website. I found this while browsing...
http://www.opensourcecms.com/
It's a site that lets you try out various CMS solutions before you go through the hassle of installing.
I plan to try Joomla first but I've been hearing mixed reviews on it myself so I'm open to exploring other options.