I'm not sure how the Moody Blues slipped my mind, but they deserve a mention as well. Absolutely love Days of Future Passed.
Also while I don't love King Crimson's body of work: 21st Century Schizoid Man is one of my favorite songs.
Can't say I'm a big fan of Porcupine Tree, although I do like the Steven Wilson remixes of classic Jethro Tull albums that amazon keeps convincing me to buy.
Based on people's lists I guess I'll have to check out Opeth, Haken, and Marillon. Haven't heard of those bands previously.
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"Ignorance may be bliss, but knowledge is power."