Come on guys! No one has yet mentioned Bernard Herrmann! Undoubtedly the greatest soundtrack composer ever. "The Day The Earth Stood Still" "Psycho" "North By Northwest" "Citizen Kane" "Journey To The Center Of The Earth" "Mysterious Island" "Sisters" "Jason And The Argonauts" "The Seventh Vouage Of Sinbad" "Farenheit 451" "Marnie", various "Twilight Zone" episodes, and more.
And let us not forget other great film music composers like Dimitri Tiompkin, Max Steiner, Elmer Bernstein, Franz Waxman, Jerry Goldsmith, and Eric Korngold.
I'm pleased to see that respondents to this post have listed real soundtracks, not pop music compliations which rule the sales charts these days.