The loss of Redding and SRV was immeasurable. Also Marvin Gaye, who died in a senseless act of violence.
The great Clarence White was killed at age 29 by a drunk driver while loading gear into his car after a concert. It’s one the most tragic losses in music for me personally because I like his playing so much, and he could have given us so much more.
Eddie Lang died from a tonsillectomy gone wrong. So did Bennie Moten. In Lang’s case, Bing Crosby had encouraged Lang to have the surgery, and he never forgave himself.
Bix Beiderbecke died at the age of 28. The official cause of death was lobar pneumonia, but his alcoholism almost certainly was a contributing factor. He suffered from delirium on the night of his death—his screaming alerted a neighbor, who came to see what was wrong. The neighbor found Beiderbecke trembling, convinced that there were Mexicans hiding under his bed with long knives. Bix collapsed, and the neighbor called a doctor who pronounced him dead.
The original Sonny Boy Williamson (not “Rice” Miller, AKA Sonny Boy Williamson II) was killed by a mugger when he (Williamson) was walking home from a gig one night.
Tupac Shakur and The Notorious B.I.G.
Not my genre, but…
Brittany Murphy was only 32 when she died. She was a popular TV and movie actress, but she was probably best known as the voice of Luann Platter on King of the Hill.
Singer and actor Bobby Darin died relatively young at the age of 37.
Singer-songwriter Jim Croce died in a plane crash in 1973 at the age of 30.
Actor Freddie Prinze killed himself at the age of 22.
Kurt Cobain committed suicide at the age of 27.
Helen Wiggin
Robert Johnson. Though he did suffer a bluesman’s death.
And for those of us old enough, the deaths of Jimi Hendrix and Janis Joplin so close to each other were very disturbing.
I’d say that the most obvious is Sharon Tate.
Another one that sticks in my mind is Heather O’Rourke.
Dimebag’s murder is still talked about a lot in metal circles.
Mike Scaccia was only 47 when he had a fatal heart attack on stage (while playing with his band Rigor Mortis, natch).
Wayne Static’s death at 48 in 2014 is currently much-talked about, since his band just released an album and is touring with someone else playing the part of Wayne, complete with a weird Wayne-mask.
Mitch Lucker’s death in a motorcycle accident was terrible and effectively spelled the end for his band, Suicide Silence.
Chuck Schuldiner was a fucking genius and he was taken from us when he was only 34 years old.
Jeff Hanneman death at 49 didn’t end Slayer, but it did change them a lot: Jeff was an amazing songwriter.
Randy Rhoads death meant that Ozzy’s material was gonna change to include lots of lame ballads.
Cliff Burton’s death meant that Metallica were gonna be a huge suck-fest forever, apparently.
And of course, D. Boon’s death at just 27 years old shattered his best friend and bandmate Mike Watt and ended one of the greatest bands to ever exist. It still upsets me to think about and it’s been over 30 years now.
Dominique Dunne (22 years old) - killed by her ex-/estranged boyfriend.
Rebecca Schaeffer (21) was murdered by a fan.
Porn actress Savannah (24) - crashed her car and broke her nose. She then, lamenting the fact that her career was probably over - shot herself in the head. To make matters worse, she was dating Pauly Shore at the time. I wouldn’t wish that on anyone.
Dimebag and Mike Sciacca were both mentioned in the Gwar cover of "People Who Died,’ originally by Jim Carroll.
ETA: this is in response to Bo’s post
Kirsty MacColl died pulling her son out of the way of a speeding motorboat in an area reserved for swimmers.
For cruel and sad I’ll have to third Stevie Ray Vaughn. He hit the depths of substance abuse and self-destructive behavior and came out the other side. His marriage ended but he seemed to have reached a peaceful place with his ex and again found happiness with someone else. He was starting to go beyond electric blues and expanding his music. It appeared that he was in a great place in his life and hitting his stride creatively. Then after a great show on an amazing tour with Clapton the helicopter hits wires.
Lennon will always be the worst for me. But Harrison was sad, too.
Ones that affected/impacted me the most:
Robin Williams - I still don’t really watch his stuff.
Anthony Bourdain - I have not watched a single episode of his shows since his death.
**Roger Ebert **- my favorite movie critic, but equally importantly, a smart commentator on life and politics. I miss him.
Anton Yelchin. His car crushed him against his own gate at the age of 27.
Pretty sure that qualifies as cruellest. 
Poor kid.
I guess at least this one lead to changes in the industry, but man.
It got even worse, in a way: the rich man who was almost certainly driving/piloting the speedboat got a member of his staff to pretend he was driving it. The law there meant that he got a fine based on his income. So he was fined €63 instead of going to prison, and paid McColl’s family US$2,150. The rich bloke couldn’t stomach admitting he did anything wrong even though he also would have avoided prison.
The rich man’s name was Guillermo González Nova. It’s a matter of public record, and I see no reason not to name and shame at every opportunity. What an asshole.
She died of complications from pneumonia and weirdly her husband passed away from the same thing five months later in the same house.
Guitarist Randy California drowned at 45 while saving his son from a rip current on Hawai’i.
Jimi Hendrix died on September 18, 1970. Two weeks later on October 4, 1970, Janis Joplin died. The close proximity of those two deaths hit me really hard, even though I was only 17.
Wasn’t he also drunk at the time?