I started listening to Clutch after hearing two tracks on the Earache Records compilation 'Naive', back in 1992. My favourites are:
Impetus EP, Passive Restraints EP, Clutch, Elephant Riders, Robot Hive/Exodus, Blast Tyrant, Psychic Warfare & Book of Bad Decisions.
All the albums have great songs on though. But some albums suffer from slightly off production (Beale St and Strange Cousins are the worst offenders for me).
Their live albums are worth listening to as they tend to spice things up a bit. They're an incredible band to watch live, as are their alter-ego The Bakerton Group.