There's plenty of classical music and operatic pieces interwoven in Hans Zimmer's Hannibal score, making a quite elegant and graceful sinister piece of work overall.
A wonderful score that I believe fits your criteria is Francis Lai's ANOTHER MAN, ANOTHER CHANCE. He blends Beethoven's music beautifully. From the liner notes - 'There's a little Beethoven and a lot of Lai, used in all sorts of interesting and different ways in the film'.
Another score that I like a lot is John Barry's DEADFALL that has his own classical piece 'Romance for Guitar and Orchestra' blended in.
