While the J2EE module reference feature allows your to create common Java library projects, I can\'t find a neat way to do this for web content.
I have common JSPs, CSS
I believe writing your own scripts (e.g. custom build steps using ant, easily configurable in eclipse) is among the more practical solutions.
You could also create multiple webapps and reference their respective resources - this would be easy with css, images and the like, not so much with jsp that need to access your code being available.
I can imagine some tricks with tomcats crossContext="true" option for the context (e.g. webapplication), enabling one application to access classes in an other application, but haven't tried them yet.
Sorry - I believe that's not the answer you'd like to hear...