Loads of early Black Sabbath stuff. A few examples such as:
Black Sabbath
NIB
Paranoid
Iron Man
Into The Void
Layla - Derek and The Dominos. Absolute killer riff
Aqualung - Jethro Tull
Since You Been Gone - Rainbow
Maybe (Don't Fear) The Reaper as well? If you count it as a riff...
EDIT: Didn't see Chilli had list DFTR. I guess it does count
