well as for Star Wars that was cut into 2 trilogy, (4,5,6) (1,2,3), Lucas considered it the Tale of Anakin and the Tale of Luke.
If there is another Halo game coming out (halo wars, or chronicles) but a new halo genre game i dont think bungie would be doing it.
For starters they said the trilogy is over and the feel that it is complete.
Second I believe Microsoft has retained the rights. (although no ones truly knows what happened to the rights) Now only way i see something happening is if Microsoft makes yet another deal with bungie to work on the Halo game.
other than that i dont see one in the near near furture.