I'm not really sure if this is really the right forum to post this question. There are so many content management systems out there it's hard to even count them and the question itself isn't really Seam related.
Depending on whether you're willing to pay money or want to go purely open source, there's all sorts of tools you might try: there's Joomla, Typo3, Zope/Plone - too many to count. If it's really just about creating content, you might give Wordpress or MovableType a try.
You probably should take a look at the backend of the tools - I guess you want to integrate it with your JEE application somehow, so the database backend should most likely be easy to understand and accessible from
outside. I can recommend Joomla and Typo3 in that regard. I'm just wondering why you're thinking about building your website with Seam to begin with - after all web content management systems usually come with some sort of templating system that takes off the burden to implement all sorts of logic; so you just build your pages with a couple of connected building blocks. No need for JEE or any complex programming there. That's just my 2 cents...
We used Seam with Alfresco WCM to build kaptest.com. Alfresco is java based and has a powerful authoring and publishing capabilities. You might want to take a look at it too.