I've had pretty good results with Usemod. This comes almost shrink wrapped - download, unzip, edit the script to tailor the data directory path, copy to cgi-bin directory, and you are away.
I've also had good experiences with Usemod - I had a site up and running in 5 minutes.
If you want something more advanced, Callisto CMS looks interesting. I've heard positive stories about its real-world use but have no first hand experience of it.
I haven't found many useful resources for comparing different CMS/knowledge management products, but CMS Info might help anyone interested in this.