Master of Reality is a GREAT album to listen while high. I got high as fukk the other night (had a strong head high), I listened to the whole album on a stereo and it blew my mind. It's also a great album sober, but when if you're stoned it's even better.
It also has a song like Planet Caravan called Solitude, which I like even more. It has a trippy psychedelic folk kind of vibe that serves as a nice interlude from the heavy tracks.