While you're at it, check http://www.seotoaster.com out, it is a free and open source CMS, and has unique automated SEO features such as automated deep links, java script link sculpting and even point and click link silo building.

It is also much easier than WordPress, as content is edited in the front-end. We believe it's the most advanced SEO CMS out of the box.

Also, agencies can private label the system, and with a subscription to SEO Samba one can remote control and market an unlimited number of websites from a central location.