My Top Ten:
Nine Inch Nails, Tool/A Perfect Circle/Puscifer (grouped together because its all Maynard the Man), Pantera, Fear Factory, Dethklok, Deftones, Five Finger Death Punch, Amon Amarth, Cradle of Filth, and System of a Down.
They're most common on my playlists on my mp3 player, computer, CD player, etc.
I'm also into Foo Fighters, Alice in Chains, more melodic grunge from my high school days. Smashing Pumpkins is a big one, as is Primus and Nirvana. There are just too many to list, really. lol