“Fairytale of New York” by the Pogues. The opening melody, which is slower than the rest of the song, does return at the end, but in the same faster speed as the rest of the song.
Sorry, I’ve never been smart enough to figure out how to label links. But this one directs you to the first song I thought of with this format. Mother of Pearl Roxy Music.
Starts off with a fast rocking’ beat and merges into a mellow ongoing groove.
I thought of “Supper’s Ready,” which definitely goes through several different subsongs in different meters and leaves most of them behind, but I’m not sure it counts, because it kind of comes back to the original tune at the end. It’s sort of a concept album in one roughly continuous track.
Just heard one that possibly qualifies. It starts as a standard soul song of the '70s, then breaks into one of the best funk grooves of that decade, Diana Ross’s Love Hangover, with the break occurring @ 1:10 into the song.
Cashman and West’s American City Suite has three parts so completely different that the end piece, A Friend Is Dying, was even played seperately as a stand-alone.
I have “The Yes Album” in my car’s CD player right now! Don’t forget “I’ve Seen All Good People/Your Move” and “Perpetual Change.” My favorite “switch” is the one in “Perpetual Change” at 7:22.
There’s also the Guess Who’s “No Sugar Tonight/New Mother Nature”.
The story behind that is that they had two songs they really liked, and neither was quite long enough to release as a single, even in that era, and since they were in the same key signature, they decided to fuse them.