I think my favourite Vangelis soundtrack is Chariots of Fire, especially the piece he composed for
this scene. It's very simple and only comes in about half-way through, but it perfectly compliments the visuals, while at the same time somehow capturing the religious motivations of the character it's soundtracking. Brilliant!
full track:
http://www.youtube.com/watch?v=Z2un1I162dw
My favourite non-OST Vangelis piece is
this though, at least from about a minute in. I remember hearing it as the sun came up during a rave, E'd off my face. One of the greatest musical moments of my entire life.