the rite of spring is more heavy than most metal bands, you can't get more metal than that! and no its not on star wars, i've listen to it in some movies but in the horror genre of course...
for more metal pieces try bartok's music for strings, percusion and celesta.
some parts of that piece are played kubrick's the shinning, its just genius!
composers you guys might check out stravinsky of course, shostakovich(middle and later period, you can't get more evil and depressive that string quartet nº15), bella bartok, allan pettersson, gustav holts the planets of course is a must Mars bringer of war is METAL!, gorecki symphony of sorrowful songs is a must for any doom lovers, barber's adagio of course and albinoni's adagio are also classic for doomers, sibelius , hell anything from the romantic period( starting of beethoven) until today might be for you !