Best band never to release a truly great album?

Yeah, I know, another poll, but these are kind of fun and this one may be a little different. Let's limit it to no earlier than the late 60's (when the album began to be more important than the single). What musician/band do you really like, but has never quite put it all together to make that brilliant album you know is in them.

I'll start by nominating Jethro Tull. Lot's of great songs, but I cannot think of a single Tull record I would call an unqualified success.