Part of the reason, it seems to me, that many artists who died tragically and/or young are revered as great artists taken from us too soon has to do with the fact that they DID die so young...they have a very mythic and magical aura surrounding their deaths AND their lives. No one knows what potential might have been explored and manifested with these people. I have more thoughts on this but that's good for now.

here's my list (must say I agree with some of those already mentioned):
my friend J.P. Slota
my friend Adam Schliemer
Jimi Hendrix
River Phoenix
Janis Joplin
Robert Burns!!!
Katrin Cartlidge (Scottish actress who died this year aged 41)
Derek Jarman (English filmmaker)
Brad Davis (American actor)
Percy Bysshe Shelley