I can't believe no one has said Kurt Cobain
Others I'd like to see - I'll give y'all an eclectic mix
Amy Winehouse
Andrew Wood - I'll second his inclusion - he was such a huge part of the early grunge
Buddy Holly
Patsy Cline
Tupac (although he also did 5 albums)
Ronnie Van Zatt
and finally....
Hank Williams - although he was well above the 4 album cut-off.... but if he hadn't died he would have cut records for decades