When I told my buddy Scott I'd been listening to a lot of Jethro Tull (so sue me, hipsters), he suggested an album by King Crimson. I obtained that band's discography and haven't listened to anything else in about two weeks.
King Crimson is a band I had definitely heard of - but unlike many other bands of their ilk (that is, art-rock bands that had their heyday in the 1970s), they don't have any radio hits. I can't think of a single one, anyway. So while I knew this band's reputation (primarily because one of their many bass players went on to be a founding member of mediocre British blues-rock band Bad Company, and Greg Lake went on to form Emmerson, Lake and Palmer, who I have never particularly enjoyed), I was unfamiliar with their music.
But it's pretty awesome, and definitely breaks the mold of 1970s art rock, jumps across genre boundaries and goes back-and-forth between what one member once angrily called "airy-fairy shit" (which I enjoy) and bombastic but cerebral heavy-riffing (which I also like).
The band has more lineups than Spinal Tap, apparently, all dominated by Robert Fripp, who, despite not having that many songwriting credits, is said to have pretty much controlled the band. The group disbanded in 1974 (having already been through a few lineups) and regrouped in the 1980s, and continues to record to this day, apparently always staying one step ahead of the curve and evolving with the times (I haven't heard it but it's reported they are deep into the drum-and-bass thing nowadays). Anyway, so far I've only delved into their 1970s catalog.
In short, I like it. A lot. My first impression was that the band sounds like a slightly happier Pink Floyd or a somewhat more pissed off Jethro Tull (interestingly, when I searched for a picture after writing this, I found this article that compares them to the same two bands). In places ("Pictures of a City") they sound like nothing so much as a very jazzy Black Sabbath. The guitar work is interesting and off-the-wall, the vocals are diverse (because of so many lead singers), and there's a improvisational jazz-fusion thing happening here that I don't quite get and don't need to. Lyrically they seem to have made strong efforts to have good lyrics (as opposed to the "I'm gonna be yer back do' man" stuff so typical of British rock in those days). The album Islands seems to be about The Odyssey, of all things.
Here's a thorough study of the band on Wikipedia.