Obvious choices - Ozzy/Sabbath, Queen, U2, Van Halen.
Ones that should be thoroughly considered - Alice In Chains, Pearl Jam, Nirvana, Beastie Boys, Pink Floyd, Motley Crue, Rage Against the Machine, Tool, RHCP.
Ones where a Pinsider can make a solid case based on genre importance, sales, and albums sold, but would the masses like it? - Soundgarden, Incubus, Goldfinger, Weezer, Green Day, Bon Jovi, Linkin Park.
Ones that are inexplicably loved bands but put out consistently horrible music - Foo Fighters, The Who.