2 utterly subjective lists, one completely mainstream, the other somewhat less mainstream, but hardly 'underground':
1. Alice In Chains
2. Black Sabbath
3. Blue Oyster Cult
4. The Doors
5. Judas Priest
6. Megadeth
7. Metallica
8. Testament
9. The Who
10. ZZ Top
1. Candlemass
2. Electric Wizard
3. High On Fire
4. Melvins
5. Monster Magnet
6. Pixies
7. Reverend Bizarre
8. Sabaton: I had to throw in some power metal, and they deserve to be on the list.
9. Solitude Aeturnus
10. Tad
But that still leaves out Katatonia, Trouble, etc. etc. etc.