Close to the Edge, by Yes (1972): Through all of Yes's legendary number of lineup changes, there are two that I think stand out as era-defining ones. The first was after Close to the Edge, when Bill Bruford left to join King Crimson (the other, if you're keeping score, is when Trevor Rabin joined up). I love Alan White's drumming and Yes made lots of good albums afterwords, but Bruford's thought that once CttE was done they'd only start repeating themselves is fairly true. Sure, Tales from Topographic Oceans went more epic and Relayer added some fusion flavor, but for the most part CttE was the pinnacle of what Yes was about. So good, in fact, that the entire album found its way onto the Yesshows live album.