With the joy that is digital cable, I just go to the 400+ channels that play nothing but music and leave it on. Found some good stuff that way. MTV 2 started off as "all music, all the time" but that turned into the second run channel of all the stuff that was MTV and is now repeating. I do like Headbangers Ball and Subterranean but I rarely get a chance to sit and watch.
Sadly, I find VH-1 Classic (cringe) to be a better station especially their "alternative" show where old 120 Minute videos are shown.