Tomcat is admittedly the reference Servlet/JSP platform, but I also like Resin from
www.caucho.com. It has more features, and they claim it is much faster than Tomcat. It's shareware, in the sense that you can use it for free, but they would like you to pay them $500 for priority support if you use it in a production system.
I've used it with lots of servers on various systems (but not IIS4, unfortunately, although they claim it works with IIS). Definately worth putting on your shortlist.