First of all, this thread should never leave the 1st page. :D
Secondly, I just picked up easily THE best book on metal that has ever been created. I am usually INCREDIBLY wary when it comes to literature about heavy metal; often the books include shitty artists and/or end up being inaccurate and outdated. However, this book (which was released in 2007), is the real deal. The book is broken down into REAL subgenres, and focuses on REAL metal bands. For example, some of the subgenres include (but are not limited to): American Thrash, UK Thrash, American Death and Grind, Norwegian Black, Worldwide Black, Doom, Power, Prog/Gothic/Symphonic Metal, Swedish, Japanese Metal, etc. The book also includes interviews, suggest which albums are noteworthy of each band, etc.
For example, here is a list of the bands listed in a particular subgenre:
Norwegian Black Metal
- Ancient
- Arcturus
- Borknagar
- Burzum
- Carpathian Forest
- Darkthrone
- Dimmu Borgir
- Emperor
- Enslaved
- Gorgoroth
- Immortal
- Mayhem
- Satyricon
Of course, a few bands that you may be looking for are left out here and there, but in my opinion, the author uses good judgment and taste in deciding what bands are included.
Metal: The Definitive Guide by Garry Sharpe-Young
about 500 pages long and $30. I highly recommend.