King Diamond, or his band Mercyful Fate, are really underrated. He's got a unique style, great voice, very good lyrics, great guitar players and a great drummer. I guess he's just not easy to get into.
Bloodhound Gang. Why are they not ridiculously famous and popular
They're as popular as they can be with those lyrics. If their lyrics were more..."friendly" they would be much more popular; but you can't play most of their songs on every radio station, after all.
So they need to be a *** group who writes songs for families and radio songs.
Look at how popular Miley Cyrus got just by doing that. She is a horrible singer, but everyone knows who she is.
Also, if their lyrics were more subtle than they are now, they could be played more. They wouldn't have to change the meaning of their lyrics; just the words themselves. Right now they're very literal and straightforward, which is why they are currently somewhat unpopular.
I think the Foo Fighters. On this site pertectually most haven't heard one song by them. So many top artists though have and enjoy touring with them. Sad because they have many meaningful songs and some very thought out ones. Most Nirvana followers on this site, however see Nirvana as the better band, even though Nirvana didn't put out to much in albums.