Back when George Bush, Sr. was in office, Dana Carvey did an impression of him on Saturday Night Live that was so memorable that the impression eclipsed the real thing. I couldn't watch a real George Bush speech without thinking of it as somehow being a second-rate Dana Carvey act.
Dave Chappelle has done the same thing to Lil John. I can't hear "what!?" or "yeaaaah!" in a Lil John song without thinking of the Chappelle version and laughing.
Free Lil' John mp3 download here.