mvn dependency:analyze | less
It will show you
unused declared dependencies, and
used undeclared dependencies so you can add or remove dependencies as appropriate. Just don't go crazy with it.
Update: (mis?)Using this introduced some problems into my code because I removed dependencies whose transitive dependencies were being used.
2014/10/10 Update: The thing to pay attention to really is the
used undeclared dependencies. They list the landmines where you are using a transitive dependency directly.