Greetings from the edge of the world.
First off, I'd like to say what a wonderful resource this site is, it has helped me discover many new bands/genres, some of which I hadn't even heard of.
I like the fact that most bands have a few streaming mp3s to give the feel of the music, so you can have a taste of the music before going out and getting more (even if most songs are better heard in the context of the album).
I "discovered" prog through a combination of Pink Floyd and Tool. There was something about those bands that seemed a little deeper and more complex both structurally and emotionally than your average modern top 40 song. Now I know it is the prog connection. I would define prog as taking pop/rock and giving it the depth of "higher" music eg. classical, jazz etc. (not that being any of those genres makes the music better by default).
Prog bands that I enjoy include: Tool, Yes, King Crimson, Opeth, Pink Floyd, Jethro Tull, Mahavishnu Orchestra, Porcupine Tree and some Genesis.
Also semi-prog bands like Muse, Primus and Led Zep.
I have dabbled in some other prog like Anglagard, Mr. Bungle, Sleepytime Gorlla Museum and Meshuggah -I am open to eclectic music in small doses.