I discovered Concrete5 (
http://concrete5.org ) a few years ago after building many Wordpress sites (large and small), and totally fell in love with it. It's not perfect, but it's
much better than any other CMS out there for end-users, designers, and developers:
* Editing UI is on the front-end -- users just go to the page they want to edit and click on things to edit them, which is much more intuitive than a back-end dashboard
* Content on pages is a collection of "blocks", so each portion of content on the page can be edited separately (as opposed to one WYSIWYG editor for the whole page). I've even built a free addon that lets designers compose their own custom block interfaces ( http://concrete5.org/marketplace/addons/designer-content ), so if you have a "employee bio block" (for example), you can have an image chooser, a textbox for a headline, a wysiwyg editor for the description, and a page chooser for a link instead of requiring the user to fidget with alignments, floats, and custom styles in TinyMCE/FCKEditor.
* Create themes from your existing design / markup -- the CMS flows around your design as opposed to you having to construct your design around the requirements of the CMS (this is much more of a problem with Drupal than Wordpress, but still gets annoying in WP for non-blog-like designs).
* Underlying architecture is fairly sane -- definitely has some idiosyncracies, but nothing like Wordpress (or Drupal or Joomla). There's a simple MVC pattern going on so you separate your model / controller / view code, and the underlying system has a decent "API" for working with pages, content, users, files, etc. Also, if you have very customized functionality, you can just create a separate page in your site and tell the system to not do anything... that you will handle everything yourself on that particular page or area of your site.
The only downside is that it's not as popular as wordpress so the documentation is lacking and there are not as many free plugins and tutorials available (but hopefully this will continue to change as time goes on).
But it has made building CMS-based websites so much more fun for me. Hit me up ( concrete@jordanlev.com ) if you want to discuss further or have any questions.