Sabin Frost
Doom makes me happy
Mayhem's Deathcrush, otherwise Smoke on the Water as Zephyrus mentioned is a good one
Edit: I largely learnt to play bass copying Peter Steele's bass lines from T.O.N so I advise you pick a band you have a strong interest in... there is no point learning to play simple yet brutal grind riffs if you want to land up playing Power Metal in the future.
Edit: I largely learnt to play bass copying Peter Steele's bass lines from T.O.N so I advise you pick a band you have a strong interest in... there is no point learning to play simple yet brutal grind riffs if you want to land up playing Power Metal in the future.