Metal is such a broad church that it's difficult to post general recommendations, but if you like riffy, sludgey stuff then I'd recommend Melvins. They're not the canonical albums, but I got into them through The Bride Screams Murder, Nude with Boots and A Senile Animal.
Boris are worth a listen too (named after a Melvins song). Maybe try Pink to start with and go from there.
If you want more tunes with your riffage, then anything by Torche is good.