Bob Dylan's release and performace of the song "Like a Rolling Stone". It completely changed the way rock lyrics were written.

Floyd's Dark Side was a MAJOR change. Not just for the group but for listener's of EVERY genre. More cohesive than the rock opera "Tommy" which was also a milestone, Dark Side is a masterpiece. I'd put it ahead of The Wall.

Elvis Pressley
Aerosmith / Run DMC performing Walk This Way
Eddy Van Halen
Jimi Hendrix
Les Paul inventing multitracking
Charlie Christian
Phil Spector's "wall of sound"
The Beatles

What about Chuck Berry or Little Richard.. Not to mention Duane Eddy, Link Wray, Dick Dale, The Beach Boys, Dylan going electric in 65 at the "folk Fest", what I like to refer to as, the "Social Change" method of songwriting that, although been around forever seemed to creep in the R and R in the early/mid 60's.

Metallica's impact on metal in the 80s and Nirvana's impact on "alternative" in the 90s.

Just a list of some of the people that have changed the world of music in some very dramatic ways. Buddy Holly (Double tracking), Chuck Berry, Elvis, The Beatles, Jimi Hendrix, Ritchie Blackmore, EVH, Leo Fender, Jim Marshall, Jimi Page Les Paul.

Chuck Berry and Elvis made it cool to play guitar with Berry being the Hendrix/VH of his day. Les Paul changed the way we recorded things not to mention the guitar he gave us. I'd have to say the Beatles were/are probably the most influential bands to ever exist. For those old enought to remember "Beatlemania" it was really something to witness. I haven't seen anything like that ever since. Hendrix changed the way guitar was played. I think he gave rise to all of those "lead guitar" over the top solos. I just don't remember too many acts doing that until he came along, then everybody was doing it. Van Halen also changed the way the guitar was played with the whole whammy bar, locking nut, hammer-on thing. Keith Moon proved that even the mentally insane could become rock stars. Cream was quite influental. The Sex Pistols brought Punk into the mainstream. MTV itself had a huge effect on how popular music was seen and heard.

Great....
Now... since this also is for Rap....

Nas's debut album Illmatic, chaged rap forever. it contained lyrics at master level, and the beats inspired many.
Nas is still tagged as the best lyric poet in rap history...

When the major racing game, "Need For Speed: Most Wanted" was released it featured a song by Styles of Beyond, named Nine Thou (Superstars Remix). everoby went nuts about this one, and it's still my favorite song today, with an electrifying flow, sick rhymes and a rocking sound.