I like Wordpress and Joomla. Both have their pros and cons.
After some initial learning I think Joomla 1.5 and Worpress are doing a very good job.
Joomla 1.0 was quite unflexible. The infinite amount of Joomla Extensions is what I like the most. And the extensions library is growing day by day.
Joomla 1.6 is still in beta and will bring some major improvements in usability and permissions.
Wordpress is improving and growing. Sometimes it's quite ressource hungry and slow.
I prefer Joomla but that would depend on the needs of the project.
What definitely needs improvements in all CMS is the Frontend GUI for the enduser/client. A client really needs a dramatically simple interface where he/she don't has to take care of tags or if to press "enter" or "enter with shift" ... which CSS file to use... how to get an article online without 20 steps... and so on....
But who knows, maybe it will come.
A real interesting CMS Project is http://modxcms.com/