The majority of the posters in this thread have pretty much summed up what you asked, but i think ill throw my input in anyway.
Camel - the first 4 albums are solid, and a must (Self titled, moonmadness, mirage and the snowgoose)...all of these have great keys, guitar, and flute interplay, and are fantastic. moonmadness is my personal favorite, key tracks being: "song within a song"...youll notice under my UM user name...and Airborn.
Genesis - Foxtrot, selling england by the pound, the lamb lies down on broadway, and nursery cryme. All 4 of these are fantastic prog from the 70s..very pretty and very artsy.
King Crimson - Absolute necesities in a prog collection would be "Red" , and "in the court of the crimson king". I also reccomend "in the wake of poseidon", and "larks tongue in aspic". very creative and entertaining...a lot of the material is quite dark too, but KC is certainly an aquired taste id say...give the stuff mulitple listens before you make up your mind.
Some other personal favorites of mine (and Mikael of opeth) would be "Cressida"...theyre jazzy prog..they had 2 albums, very good stuff. "Gracious"...another band with 2 great albums of prog with some popish elements, but done tastefully and well...very 70s stuff there. And If you like concept albums i would really reccomend Jethro Tull - Thick as a brick album....and Yes - Close to the edge (one of my top albums of all time). Yes and Rush's 70s work is my favorite music ever at this point...i couldnt reccomend that stuff enough. Id check out Rush - 2112 and hemispheres albums.
Well, i hope this stuff helps you out...Prog is an amazing and exciting genre of music, get lost in it...and enjoy yourself.
