This is really hard. I've tried doing something like this before but I can never really choose a favorite over the other especially among my top 8-10. And I'm assuming we're only allowed to choose one album per band, which is even more difficult. Then I have to take into account different subgenres, which to me is like comparing apples to oranges.
But...here goes.
20. Motley Crue - Shout at the Devil
19. Scorpions - Love at First Sting
18. Immortal - At the Heart of Winter
17. Queensryche - Operation Mindcrime
16. Iron Maiden - Piece of Mind
15. Suicidal Tendencies - Lights...Camera...Revolution!
14. Death - Symbolic
13. Gorgoroth - Antichrist
12. Moonsorrow - Voimasta Ja Kunniasta
11. Korpiklaani - Tales Along This Road
10. Turisas - Battle Metal
9. Finntroll - Jaktens Tid
8. 1349 - Hellfire
7. October Tide - Rain Without End
6. Darkthrone - A Blaze in the Northern Sky
5. Paradise Lost - Draconian Times
4. Opeth - Orchid
3. Satyricon - Nemesis Divina
2. Katatonia - Dance of December Souls
1. Mayhem - De Mysteriis Dom Sathanas
And then there are all the albums I like from a lot of other bands who I wouldn't say are among my most favorite bands, but who have made some killer music (like Enslaved, Dream Theater, Annihilator, Skyforger, WASP, Skid Row, Eluveitie, and so on...and so on...)