Black Sabbath
Sleep
Electric Wizard
Church of Misery
Metallica
I can't remember the last time I actually listened to Metallica, but they get put on the list purely because of their influence on me as a kid. Growing up in a town of 500 people in a time before internet, I listened to what was on the radio. Metallica was as good as it got for me back then. They started my obsession with music. So alas, #5 on the list.
At 14, a friend introduced me to the "Garage Days Re-revisited" Ep.
To this day, I think it is some of the finest work of any heavy band. Classic covers done quickly, with obvious drive, energy, and a healthy dose of fun. This after the tragic loss of Cliff.
I never ever get bored with that EP. Have it on CD, Vinyl, and Cassette.