I'm in the process of trying to put together a prog rock mix disc (or two) for a friend of mine, and I find that's it's very difficult to do. I'm afraid to put on some of the more outrageous examples of the form - Van Der Graaf Generator doesn't have anything in their catalog that I would consider an 'entry point.' But, at the same time, if you don't put anything, you know, prog on it, it really isn't going to be representative of the genre.
My solution (I think) is to make a three disc set - one that covers the poppier end of the genre, one that is all about the soft and introspective end, and one that's a full-on deep end of the pool 'I bet you didn't know music could get this ugly' mix. At least that way the discs won't be uneven in tone. Now I just have to see if I can find enough material to fill three discs. Thank Steve that prog is a genre littered with single songs that fit on what used to be an entire album side. Heck, I could end up with a mix that's three CDs containing a total of 9 songs.
Now that's what I call music.