O.K here are my two cc's
Pantera-most songs on Great Southern Trendkill, all thier stuff is great but Trendkill is just off the charts for aggression.
The obvious ones everyone has mentioned already (Metallica, Megadeth, Slayer, etc.)
What I have not seen is a band that I suggestfor anyone training or going to war----- Pro-Pain, mostly anything from them, good starters are Foul Taste of Freedom, Death on the Dance Floor, Murder 101, Pound for Pound. All of the newr stuff is great too, it's just too much to list, but everyone check them out.