There are a couple of options...
1)
Lomboz plugin allows development of Web applications, including J2EE applications. Supported servers include JBoss, WebLogic Server, Tomcat, JOnAS, JRun, and almost any J2EE compliant server. It also has support for XDoclet code generation, etc.
2)
Sysdeo is more of a Tomcat specific plugin. It is used primarily for building web-centric applications for hosting under Tomcat, and as such is pretty light-weight and easy to use.
I haven't used Lomboz at all, but I have used the Sysdeo plugin and it works very well. Once you configure it for the location of yout Tomcat instance, you can start and stop the server right from within Eclipse and have access to all of the debugging tools in Eclipse (even to debug Tomcat itself).