Well, Mastodon sorta reminds me of Rush meets Slayer. No Cookie Monster vocals, a la "Cannibal Corpse," et al.
High on Fire features the bassist from Melvins, sounds a lot like that band as a result, and also reminds me a lot of Motorhead.
I wouldn't recommend a lot of new metal, but I was quite the Anthrax/Metallica/Megadeth/JP/Iron Maiden fan way back, and both of these bands appeal to me.
YMMV.