Rachmaninoff's 2nd Symphony 3rd movement is the pinnacle as far as I'm concerned. As for "pop" music, off the top of my head I think of "When We Dance" by Sting, but there are many others. Then there is the achingly beautiful compositions in the filmusic genre. Bernard Herrmann's love theme from "White Witch Doctor" (get past the title) or finale from "Fahrenheit 451"....and there is Victor Young's hearbreakingly beautiful love theme from "The Left Hand of God" or Franz Waxman's theme from "Peyton Place" or Alex North's deeply emotional theme from "Spartacus."
