You could take a look at FeinCMS for Django. But seriously with Rails or Django - especially Django due to the admin site - a bespoke CMS is a fairly trivial endeavour. My initial CMS took a couple of days and it's been easy to extend it for every site that's come along since.

It's a hell of a lot easier for end users than Wordpress and as it's bespoke for every client, they never get clobbered with chunks of the admin that bear only a loose relationship to their own content.