I guess you allude to the obvious ones, the '59 Holly-Valens-Big Bopper crash and the '70-'71 wave that hit Hendrix-Joplin-Morrison, but let me offer two more:

Jim Croce-Poor guy's career was really starting to take off too, could have been folk singer for the ages

Robert Johnson-Just about every musician in awe of this guy's talent, mystical life and early death in 30s, inspiration for many a 60s blues or rock tune.

Otis Redding-"On the Dock of the Bay", his biggest hit, recorded a few days before his untimely death. I get teary-eyed every time I listen to that...

Tammi Terrell-Watch "Ain't no Mountain High Enough" with Marvin Gaye at:

https://www.youtube.com/watch?v=IC5PL0XImjw

...and know that Tammi died a brain cancer death not long after. To think of both Terrell and Gaye is doubly sad. You can't help but wonder if she'd have been as famous as Dianna Ross. This is the only version of "Ain't No Mountain High Enough" I can stand to watch, the others all seem like cheap imitations!