Looking for a new good CMS

[Hawke]

I've come to the realization that a website I maintain needs a new content management system. I have been running it on MD-Pro, which isn't the most standards-compliant system out there.

Can anybody out there recommend a good, clean, extensible content management system (I'm looking at you, Paul!) ? I'm looking for something written in XHTML/XML, with XML/CSS templating management (no using tables for site layout...bad!).

Further, I require: Hierarchichal member management, news management, article management, mailing list management and a forum.

I suppose I should add that I'm looking for an open-source system.

Thanks!