ANT Build Utility
I prefer the ANT build utility when developing Java, JSP and Servlet based applications.  The main reason for this is because I develop on a diverse assortment of environments and operating systems.  Which, if not for ANT, would force me to acquaint myself with the capabilities of a different IDE per application.  Another benefit of using a build utility like ANT is the ability to add functionality such as Unit Testing to the build process.