Nirvana is actually considered "Grunge" along with a few others (Like Pearl Jam). I don't see why you felt the need to add them to the list, but whatever jingles your bells...
I would say Metallica as well. They are a great band with guys who are just too good at their instruments. Anyone who has seen these guys effortlessly solo while they sing knows what I mean.
Of course you have to give the originals the props for starting the whole thing. Sabbath, Megadeth, Maiden, they're all great bands on a gigantic scale.