Ah, the dead ones. More hilarious, and proven more true as time goes by...RIP.
That said,
Richard Pryor
George Carlin (the only "old-school" not sidelined or dead, and really 2 in 1--the counterculture, language-obsessed hippy of the 1970's and the incendiary [really p*ssed off?], atheist, and still language-obssessed observer from 1990-present)
Chris Rock
Dave Chappelle (somewhat less since the discovery of Pryor)
for some unknown reason, Ron White