Impossible to pick just one, so I'll just list a few:
Tool, Alice In Chains/Jerry Cantrell, A Perfect Circle, Metallica, Led Zeppelin, Floater, Pearl Jam, Springsteen (older stuff), Nine Inch Nails, Opeth, Porcupine Tree/Steven Wilson, Soundgarden, Comes With The Fall, Rage Against the Machine, Jinjer (I just discovered this band through a friend and am really loving them), Isis, Neil Young, Sage Francis, Les Claypool...I think I'll stop now.