Acoustic Strawbs "Baroque and Roll" is fantastic. Several bands have good "mostly" acoustic songs mixed oin on their albums - including Porcupine Tree, Rennaisance, Illusion, and Mostly Autumn. Anthony Philips stuff is good. While they're not exactly Prog, The Pentangle is all acoustic and I think they appeal to Prog fans. I don't know of any acoustic King Crimson, but if that's what you're looking for try California Guitar Trio - "CG3+2". It has some KC, Yes and similar original material. And if you're looking for Dream Theater - try "An Evening with John Petrucci and Jordan Rudess" - it's live, all instrumental, and "somewhat acoustic".