Princess Diana?
John Lennon seems to be defined as much by his death as his music these days.
And this seems appropriate for this thread.
Certainly fits this part of the OP:
I pretty much always think about how sad her death was when I see anything in the media about her.
And Bon Scott (perhaps debunked, some people claim it was an heroin overdose).
My contribution: Danton. Robespierre wasn’t bad either. Hitler and Goebbels… I don’t know whether define is the right word, but their deaths were in character. And Goering’s too, come to think of it.
ETA: Mussolini!
Boy, I don’t agree. Also disagree about Elvis.
Most of the others in this thread I can get behind.
We just watched Clueless last night, so of course I immediately thought of Brittany Murphy. Her strange, mysterious death gets more attention than the few roles that she was in.
As you can guess from my reply in the other, related, Cafe Society thread, I agree with you on this.
Mostly because Elvis shouldn’t be included in this thread until he dies. 
Joseph Patrick Kennedy: He was supposed to be the Kennedy who would be president, but he died in WWII in a bizarre and highly risky attempt to fly a radio controlled bomber into a target - a very early ‘drone attack’. Kennedy was supposed to fly the bomber to altitude, arm the explosives and bail out, then a chase plane would fly the bomber into the target remotely.
Unfortunately for him, a likely wiring issue caused the explosives to detonate shortly after he threw the arming switch, killing him and his co-pilot instantly. And that’s about all he’s known for now. He was awarded the Navy Cross.
Probably a good thing anyway. He was fan of Hitler’s before the war, and especially his eugenics program, which he wrote to his father would, “do away with many of the disgusting specimens of men.”
Better to be remembered dying heroically.
Yeshua ben Yosef (aka Jesus H. Christ)
Michael Hutchence intentionally killed himself by hanging. Nearly all deaths from things that people don’t actually die of like “autoerotic asphyxiation,” “toxic mold,” “cleaning their gun” etc. are either suicides or drug overdoses, with stories conconcted from family members in denial or people who are afraid of being blamed for supplying drugs or such.
I didn’t know about this but her widower dying in the same way within a year is pretty bizarre.
Lee Harvy Oswald. Along with JFK, their deaths still puzzle us to this day.
Yeah, this one comes to mind - stupid fascist, killed and his corpse publicly hung upside down for additional humiliation. You’d think this example of what happens to fascists would be remembered.
Also, Nicolae and Elena Ceaușescu of Romania, executed after a show trial by firing squad in 1989.
The Apollo 1 astronauts. Gus Grissom was the second American in space and narrowly escaped death at splashdown, but even that was overshadowed by his and his crewmates death by fire in a pre-launch test.
And of course the two Shuttle crews that were killed in flight.
Charles Lindbergh, Jr. (the Lindbergh baby).
JonBenet Ramsey
His death was nothing to write home about, particularly at his advanced age, but if it is the funeral that counts, I will add Ayatollah Khomeini.
ETA: How could I mention Danton and Robespierre and forget Marat?
Now I think I have a political bias today. Ah, well…
The main cast of Rebel Without A Cause - James Dean (car crash), Natalie Wood (drowning), Sal Mineo (murdered by random mugger) all relatively young - 24, 43 and 37 respectively.
Can’t watch or even see a reference to the movie without someone mentioning that the 3 leads all died young.
Thích Quảng Đức.
86 floors? How the hell did her body remain intact and bloodless? I would think you would be ripped into pieces and completely mangled after a fall of that height.