Here is my top 10 list(ok it's a little more than 10)of influential artists and why they're influential:
The Beatles-Forget how many albums they sold for a minute,they revolutionized the way songs were written,they changed the way music was made in the studio,it was through them that music grew a social conscience,they encouraged their contemporaries(and those who followed them)to express their opinions on relevant issues of the day.I could go on for awhile about what The Beatles did for rock and roll other than sell a lot of albums.
ELO-Their fusion of rock and classical music,yes The Beatles were among the 1st to use classical instruments on pop/rock songs,but ELO took it to the next level!
The Who-Considered by many to be the godfathers of punk,also put out the 1st album that told a story(Tommy)
Pink Floyd:All I have to do is mention 2 albums:Dark Side of the Moon and The Wall
The Beach Boys:All I have to do is mention one album:Pet Sounds,in fact Paul McCartney has been quoted as saying that if not for Pet Sounds,there would've never been a Sgt.Pepper
Bee Gees-Helped usher in a cultural revolution in the 1970's
The Rolling Stones-Albums like Beggars Banquet,Sticky Fingers,and Exile on Main St. have shown why the Stones earned the title "World's Greatest Rock and Roll Band"
Led Zeppelin and Black Sabbath-I put these 2 bands together for a reason because they are considered by many to be the founding fathers of heavy metal
The Kinks-Although Zeppelin and Sabbath are considered to be the founding fathers of metal,it was You Really Got Me that was a huge influence on them and other bands(like The Beatles),in fact You Really Got Me is considered to be the 1st metal song
The Byrds-1968's Sweetheart of the Rodeo inspired bands like The Eagles,Poco,and The Stone Canyon Band,in fact it was this album that gave birth to the country/rock genre
The Yardbirds-Particularly while Jeff Beck was a member,listen to songs like Shapes of Things,I'm A Man,Heart Full of Soul,Evil Hearted You,and Still I'm Sad
Cream-Their pioneering fusion of rock,pop,jazz,and blues
Nirvana-As The Beatles and their British Invasion cohorts swept away the teen idols of the late 1950's and early 1960's,so to did Nirvana and their grunge brethren swept aside the hairbands and power ballads of the 1980's.
The Moody Blues-All I have to do is mention 1 album:Days of Future Passed
The Doors-One of the 1st to really write from the dark side of music,I highly doubt that any other band would've had the balls to write a song like The End or defy an order of The Ed Sullivan Show!