ok ill take this on.....1969...because it still had very good albums and or songs from previous generations and had definative albums from all the top bands that would consolidate and then define the sound for generations to come.. ()ok I knoe that sounds like an old timer on a classics radio station but you take my point...its hard to pick 80's or later bands because they are so derivative of what came before, but I am sure i will get challenged on that front )
so ;
Beatles - abbey road and arguably let it be also..
Stones let it bleed
the who - tommy
led zepillin - I and II !!!
dylan- nashville skyline ( granted not his best but highly underrated)
Neil Young- everyone knows this is nowhere
velvet underground - self titled
fairport convention- 1st 2 albums!!!!
creedence clearwater --3 fucking albums!!!!..bayou, green river and willy
nick drake- 5 leaves
presley- suspicious minds , in the ghetto....
Neil diamond- sweet caroline
Johhny cash- a boy named sue
CSY- CSY

probably more if i think about it