I checked out wookiepedia about force ghosts and Vaders Ghost is apparently unique in that he did not make himself a ghost Obi-wan and Yoda did so he could complete his training, which is the official explaination anyway. So it's Dead Sith to become Dead Jedi with a little help from others.
Maybe we could play With A Little Help From My Friends as Anakin's ghost appears. Though I would suggest we use the Joe Cocker version rather than the Beatles...Otherwise it might come off as a little silly.