The Beatles, not Elvis, he eventually tried to get The Beatles "banned" from the United States, and The Rolling Stones were just The Rolling Stones, so The Beatles win!
seriously, greenday? no way, they're not even the greatest punk band ever, maybe of the last 10 years, but ever? hell no. I would either The Sex Pistons or The Ramones.
Greatest Band Ever = 1) Beatles 2) The Sex Pistons 3) Nirvana
Pop: Michael Jackson (I hate to admit it...hate that guy)
Metal: Black Sabbath
Rock: Led Zeppelin or The Beatles
Country: Johnny Cash
R&B/Hip Hop: Run DMC
Celtic: The Chieftains or Stan Rogers