It’s kind of cool to like heavy metal these days.  If you’re looking for a way in, you might want to read Metal : the definitive guide : heavy, NWOBH, progressive, thrash, death, black, gothic, doom, nu.  Written by Garry Sharpe-Young (of Rockdetector fame) this book blends biography, history and criticism.  Arranged by genre, each category features a description of the sound and band profiles with discographies.  Unlike other celebrations of the style, this book takes an international perspective and covers lesser-known acts around the world. 

If your interest is raised, Ian Christe’s Sound of the Beast explores the evolution of heavy metal and its continuing popularity with each generation.  If you want to see and hear your metal heroes, I can’t recommend highly enough Penelope Spheeris’ documentary on the 80s metal scene Decline of Western Civilization Part II : The Metal Years.  Sure parts of it are staged, but it’s a fascinating and at times poignant look at metal’s winners and losers.