The classic sounds of '70s hard rock and heavy metal have never gone out of style (that's why they've earned the tag of "classic"), but although each subsequent generation has offered up bands eager to tap in, recycle, and reinterpret these timeless teachings, this enduring "retro" tradition has gained an especially large and dedicated legion of believers in the 2000s. So much so that for every band looking to the predictable Sabbath/Zeppelin/Aerosmith axis for inspiration (see Wolfmother, Witchcraft, The Sword, etc., etc.), there are others digging through forgotten crates to...