Floyd may have turned the '70s rock song into high art, but they proved just as influential as sonic explorers. The mind-warping “Interstellar Overdrive” helped launch improvisational psychedelia and the use of atonal feedback, while the ethereal “Echoes” boasts otherworldly harmonies, giving birth to space rock and ambient pop. Another game changer is the dystopian “Sheep”—icy, synth-based art rock.