SuperSeventies has a nice index of the top ten songs of each year in the decade I discovered music.  That was mostly via radio, and that decade saw quite a shift in popular styles, as you can see at the link.  Each song is linked to an informative bio, with links to other information.

I was surprised to learn that John Denver's hit "Sunshine on My Shoulders" was conceived for a made-for-TV movie.

The feature was called Sunshine, and was a character study based on a real-life journal excerpted in the Los Angeles Times. It told the story of a terminal cancer case: a nonestablishment couple and the doctor who tried to save the young woman. CBS drew high ratings when they aired the film on November 9, 1973.

The soundtrack version was re-recorded in time for Denver's greatest hits album, and became his first number one hit.  For my money, his best song will always be "Rocky Mountain High."

Link