Savatage early materials, Satan UK, Avenger (UK), Slayer(USA TX),  Oz(SWE), Flames of Hell (ICE), Savage Grace (CAN), Omen(CAN), Anvil(CAN), Exciter(CAN), Razor(CAN), Meliah Rage(USA Boston), Judas Priest, Iced Earth, Leatherwolf, Raven (UK), Fates Warning, Helloween early materials, Shellshock(Japan), Talon(USA), Queensryche very early, Riot (USA), list is huge

Best Power Metal bands in english are Helloween and Stratovarius i think.
In spanish for me maybe WarCry and Avalanch.

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The life i try to give is all i have inside of me, it's one kind of life for me this music you hear, the strenght we have inside is so much more than you will know, but if you can't see the life around
You'll always walk alone - Helloween

Agreed Pantera

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Iron Maiden, Judas Priest :P
 
As for slightly newer ones Helloween, Stratovarius and Rhapsody are the best. Also Sabaton.

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When in Danger or in doubt,
Run in circles, Scream and shout.

 
How on Earth is Slayer Power metal?! ...or Pantera as a matter of fact

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When in Danger or in doubt,
Run in circles, Scream and shout.

it will be Nocturnal Rites, HammerFall, Stratovarius and Sonata Artica....

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MetalHeads were HairyBlokes Not skinny Emo Feminine kids

This is my TOP 20 best Power Heavy Metal band.

1. Hibria (Brazil)
   
   
2. Rhapsody Of Fire (Italy)
   
   
3. HammerFall (Sweden)
   
   
4. Savatage (United States)
   
   
5. Symbols (Brazil)
   
   
6. Primal Fear (Germany)
   
   
7. Stratovarius (Finland)
   
   
8. Yngwie Malmsteen (Sweden)
   
   
9. Helloween (Germany)
   
   
10. Hangar (Brazil)
    
    
11. Judas Priest (England)
    
    
12. Edguy (Germany)
    
    
13. Iced Earth (United States)
    
    
14. Sonata Arctica (Finland)
    
    
15. Blind Guardian (Germany)
    
    
16. Angra(Brazil)
    
    
17. Twilightning (Finland)
    
    
18. Dark Moor (Spain)
    
    
19. Lost Horizon (Sweden)
    
    
20. Shaman (Brazil)

Excuse me but it is impossible to choose a single band.
Wherefore, I created my favorite list...

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Yay! My second favourite band of all time!

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maybe it hasnt gotten clean vocals but i still rate it as my favorite heavy/power band 3 Inches Of Blood

Definitely Mercenary (DNK)

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Last.fm: Mercenarion