One thing I'm surprised about in these forums is that there is not much discussion of lyrics. My opinion is that good lyrics are necessary (except for instrumentals, of course) for any good song, prog or not. While I love Eddie Van Halen's guitar playing, for example, I'm not a VH fan because their lyrics are generally lame.
I'm not a big fan of "fantasy" type lyrics, such as Yes or Glass Hammer. The lyrics need to touch me in some way, either emotionally or politically.
My favorite lyricist, bar none, is Fish. His lyrics hit home with me during a tough time in my life, and the emotion he has put in many of his songs has made him a regular purchase of mine. Unfortunately, IMO, his music has not always matched his lyrics.
Among my favorites, from Marillion's "Warm Wet Circles": "She faithfully traces his name/With quick bitten fingernails/Through the tears of condensation/That will cry through the night/As the glancing headlights of the last bus/Kiss adolecense goodbye".
What other lyricists strike peoples' fancies, and why?