To be honest, I'm so lukewarm on metal as a genre nowadays, I don't even want to name a band.
My favourites would be:
Black Sabbath
Rage Against the Machine
Opeth
Machine Head
Tool
Why Iron Maiden get so much love in the metal community, I'll never know. A lot of their stuff is as bad as power metal, and the little I can stomach, I can only enjoy by approaching it almost like a well-executed parody of good metal.