bill - 9:19 am on May 17, 2005 (gmt 0)
I've used MovableType to make 100% validating XHTML / CSS sites that certainly aren't blogs. I use it as a CMS on a number of sites. There are a few more validating CMS packages out there now that I've read about, but a lot of it seems to come down to your familiarity with the software and your ability to manipulate their templates. As long as you can control what goes where, and how it's all output, I'd say that's your best bet for SEO in a CMS.