recommendations for a web CMS (content management system)?

[Joe Strout]

We need to set up a content management system that allows nontechnical  
users to manage the content of their web site.  Rather than starting  
from scratch, I'd prefer to start with an existing CMS that we can  
extend as needed.  So, I'd prefer something with nice clean, easy-to- 
follow code over something that includes everything but the kitchen  
sink.

Any suggestions?

Thanks,
- Joe