Metal Kult has a series of videos with Matt Pike from High On Fire showing how to play a bunch of riffs from their songs. Don't much care for the finished product of the albums (Death Is This Communion is the latest), but his guitar playing by itself sounds great. He's got a very different style than anybody I've seen - lots of slides and power chords, but he ends up with a very fat sound (the 9-string First Act tuned down 2 steps doesn't hurt).