I am seriously impressed there is no mention of "Jesus Christ Superstar", this is my first choice.
Gladiator pushed Lisa Gerrard into mainstream and stardom but any Dead Can Dance album, with Brendan Perry baritone diluting her wailing is much more listenable all the way thru. If in doubt, just listen to Lisa Gerrard with Klaus Schulze albums: too much of a good thing is too much for me.
Tangerine Dream soundtrack and Zabriski Point share the bronze medal in my collection: far from the best but I have to bow to my fav groups ;-)