Emerson, Lake and Palmer. See https://www.youtube.com/watch?v=WKNOlDtZluU for some of their bigger works, https://www.youtube.com/watch?v=iL7p86-2mPo for something more classical sounding (ok, Xenakis), and https://www.youtube.com/watch?v=U7NAGTq_IJQ for an entire orchestra being replaced by three guys and a Moog.