Try Black Sabbath's NIB (main riff), Iron Man (main riff), Black
Sabbath (opening riff)
Candlemass' Solitude (main riff, second riff)
Deep Purple's Space Truckin' (main riff, chorus riff), Black
Night (all)
Dio's Holy Diver (opening riff)
Danzig's Twist of Cain (opening riff; it's easy but fast)