Of the Classics I would have to say a close tie between Led Zeppelin and The Beatles.
Contemporary, Nirvana, and I really admire Radiohead. A personal fave of mine, well Nirvana I guess, brings back memories, just like Floyd!!!

__________________
who are you and who am I
to say we know the reasons why
some are born and some men die
beneath some infinite sky...
so all things time will mend
so this song will end

Gilmour in 'Childhood's End'