I can't believe no one has mentioned The Moody Blues in this thread yet.
And one I want to throw in. There are always bands that people try to cut out. Stone Temple Pilots were always labelled as a Pearl Jam knock off or imitators of insert name here grunge band. Why? I guess not being from Seattle was strike one. Strike two was they made some songs that became huge hits and were over played. (speaking of over played, I despise Nirvana and would be content to never hear them again). Strike three... not certain here. I guess strike three is Weiland hasn't ended up dead after his drug problems like all the people that are labeled as the grunge greats. Once you dig a little some of the songs are fantastic. DeLeo's guitar sounds like most other grunge but there's so much more going on than the power chords used by most of them.