Hmmm...interesting category. It's kind of vague as to what you're asking because for example, there's a lot of metal that naturally goes undiscovered because metal is not a mainstream musical genre by any stretch of the imagination. For example, have you ever heard of Napalm Death? Well, they're one of the better grindcore/death metal bands, but only a fraction of a general music audience is familiar with that. Shoot, even one of the pioneers of death metal naturally called Death isn't generally known, but is one of the more important bands in the course of metal history.
With that said, in no apparent order...
1. Death By Stereo - Getting It Off My Chest
2. Pissing Razors - Between Heaven and Hell
3. Dust to Dust - New Low
4. Celtic Frost - Circle of Tyrants
5. Bathory - A Fine Day to Die
6. Prong - Snap Your Fingers, Snap Your Neck (even if Prong have a cult following)
7. Napalm Death - Puritanical Punishment Beating
8. Drain STH - Simon Says (unless you own the ECW soundtrack, you don't know this
9. Exhumed - Death Walks Behind You
10. The only non-metal song of the bunch: Swamp Candles (ECW Blue World Order theme song)