Ribbon - Free CMS made simple Theme
Note1: It has only one-level menu (not suitable really for a CSS-menu..).
Note2: There is an extra content-aria in the right sidebar
Very easy to install: Just upload the XML-file through the Theme Manager, activate the template(s) and off you go.
Tested with CMSMS 1.7.1 in IE8. FF 3.6.3 and Opera 10.53