Pink Floyd. Started off as whimsical psychedelic material with Syd at the helm, then after spinning their wheels for a while trying to find their niche (even though Atom Heart Mother is a favorite of mine, it's totally transitional), they really come up with what we consider the classic Floyd sound with Meddle, and with that you get through the 70s with six classic albums. Yeah, I'll count Obscured by Clouds as an underrated classic. Nobody gives it its due.
Radiohead. After being written off as a one-hit wonder with "Creep" being amidst a bunch of shitty songs like "How Do You," "Prove Yourself," and "Anyone Can Play Guitar," they keep their heads above water with The Bends (which apparently got overlooked initially) and then OK Computer put them in the pantheon, and so on. Even though some of Pablo Honey isn't so bad, a lot of it is pretty uninspired, and I'll take any other era over that one.