IMO the most important songs by decade:
50s - Rock around the clock. Perhaps the most important song in Rock n Roll history.
Johnny B Goode, Tutti-Frutti, Hound Dog, That'll Be The Day, Earth Angel.
60s - I Want to Hold Your Hand. First hit Beatles song (in the states) and the start of the British invasion. And the first of 7 number 1 songs for the Beatles in a one year time frame. In April 1964 the entire top 5 was made up of Beatles songs.
Respect, I Heard it Through the Grape Vine, Good Vibrations, My Girl, Like a Rolling Stone, Satisfaction, My Generation about about a thousand other songs. Certainly the greatest decade in music.
70s - Night Fever - Bee Gees biggest disco song, although Stayin' Alive maybe their best.
I will Survive, best disco song of all? Hotel California, Stair Way to Heaven, My Sharona and Just What I Needed for bringing about an end to disco.
80s - Billie Jean - Billie Jean is what made Michael the biggest star of his era. It was the song that catapulted him to the top. It was this song that made Thriller the biggest album of all time.
Lucky Star - Madonna's first hit, Don't You Want Me, one of the first and more important synthpop songs and synthpop was probably the most important genre of the decade. I Ran (So Far Away) - the first song to become a hit due to MTV and videos, Take on Me, Money for Nothing, Rio and a few other songs that really made videos what they were.
90s - Macarena? Second biggest hit of the decade (One Sweet Day was biggest) plus it shows that the 90s was a bunch of nothing in which no one genre dominated.
Other suggestions: I Will Always Love You, cast a long shadow over the decade. Wannabe - Spice Girls (started the whole girl/boy band thing that dominated the end of the decade) Gangsta's Paradise - one of the biggest rap songs of all time and one of the key songs to help rap cross over to mainstream popularity.
