Deimos:What about Kyuss eh?
Sure, if you put their riffs under a microscope there's nothing special but they do have a great fucking sound and tone to them.
I could never get the sound out of my guitar that they get, playing drop C feels like jumping friggin' rope (boing-boing-clang) 
EDIT: Since when did "fucking" stop being auto-censored!! that's fucking awesome!
I think Kyuss is in C standard tuning, but I'm not sure since my ears totally suck. Gardenia, Writhe, Thong Song and that huge riff before the solo in Demon Cleaner are all awesome.
Alice in Chains:Them Bones, Rooster
Black Sabbath: Chorus riff to Killing Yourself to Live
Moterhead: (We are the) Roadcrew
Jimi Hendrix: Purple Haze (my favourite)
Theres tons more but............................
BLUB BLUB BLUB