Actually, I have another vote for the saddest song ever recorded. It's Randy Newman's "God's Song (That's Why I Love Mankind)", which is certainly worth a listen:
https://www.youtube.com/watch?v=C0TvfqmWf4M
Update: I see I posted this right at the start. Oh well, it's worth posting twice. For a happy song, how about The Beatles' "It's All Too Much," which I believe is Harrison?
https://www.youtube.com/watch?v=2zc3idF_IZ0
Cheers,
John