for me the music is the highlight of the movies. It's probably why i like the prequals better. Thought the acting may not be that great, williams has grown as a composer tremendously since the first 3. My fave theme is probably what I call the "Chant of the Sith" it's what plays for the emperor and I don't know the actual name. I've heard lucas say that he writes his movies to music and then tells williams what he wants to hear. so i'll make a prediction based on his use of Stravinsky's the Rite of Spring when writing episode 4. The Obi-wan/vader duel in ep 3 will have music reminiscent to the sacrificial dance in that ballet.
i think someone already mentioned this, but a duel of the fates played two octaves lower at durge pace would be nice for the ep 4 vader/kenobi duel. also, how about some nice duel of the fates chanting ala ep 1 for the scene in ROJ where vader finds out about leia.( Oshinanta...Koratama). oh and a louder choral crecendo when palpatine is vaporized