Heh, I opened this thread as I was listening to "Mad Man Moon". I'll never forget when a friend introduced me to Peter Gabriel-era Genesis. Having only heard their later crap like "I Can't Dance", I thought he had to be kidding. I sure was surprised. "The Lamb Lies Down on Broadway" is my all-time favorite album.
Looking thru my current Winamp playlist, I'd make a prog mix CD out of:
Supertramp - Hide In Your Shell
Elton John - Funeral For a Friend (it's a damn shame he didn't do more stuff like this)
Dream Theater - The Spirit Carries On
Genesis - Broadway Melody of 1974 (what a kickass song)
Gentle Giant - Peel the Paint
Peter Gabriel - Moribund the Burgermeister
Pink Floyd - Pigs
Traffic - Low Spark of High Heeled Boys
Yes - Starship Trooper
You guys should check out
www.uk70s.com - it's a streaming radio station that plays all kinds of older prog rock. There's always a lot of early Genesis, ELP, King Crimson, Gentle Giant, Yes, Jethro Tull, and other great stuff. It's pretty much all I listen to at work.