And don't forget Resin (from
http://www.caucho.com ) and Jetty (from
http://jetty.mortbay.com ). Both are high quality standards-compliant servers with full source code available for free.
I personally use Resin, and many people find it faster to use and easier to install and configure than Tomcat. Javawebserver is not really standard enough, so I would not recommend using it. Tomcat is the official reference platform for the Servlet and JSP APIs.