I picked Great Gig, but I really like Any Colour You Like and One of These Days, too. Any Colour has that free sounding, funky beat to it, and there are only two chords for most of the song, so there's ton of room for improv. I play it on my piano all the time, and it's a favorite of some of my "fans" (mom) and it never sounds the same when I play it. One of these Days was the song that got me into Pink Floyd, since I heard it sounded like the Dr Who theme, so i checked out the live BBC version and I really liked it.