As we see from the table below, Metallica counts 6 wins, Slayer 2. Dominance of US bands. All but one big British bands have made it: Sabbath, Ozzy, Motorhead (covering Metallica) & Priest. Thus a Maiden win would be possible. But it would have been the second in a row for a Brit.
Maiden had two other nominations (FotD, Wicker Man), while Megadeth seven!! Both never made it. Thus I give some more possibilities to Megadeth
1990 Metallica United States One
* Dokken – Beast from the East
* Faith No More – The Real Thing
* Queensrÿche – "I Don't Believe in Love"
* Soundgarden – Ultramega OK
1991 Metallica United States Stone Cold Crazy
* Anthrax – Persistence of Time
* Judas Priest – Painkiller
* Megadeth – Rust in Peace
* Suicidal Tendencies – Lights...Camera...Revolution!
1992 Metallica United States Metallica
* Anthrax – Attack of the Killer B's
* Megadeth – "Hangar 18"
* Motörhead – 1916
* Soundgarden – Badmotorfinger
1993 Nine Inch Nails United States Wish
* Helmet – "In the Meantime"
* Megadeth – Countdown to Extinction
* Ministry – "N.W.O."
* Soundgarden – "Into the Void"
1994 Osbourne, Ozzy United Kingdom I Don't Want to Change the World
* Iron Maiden – "Fear of the Dark"
* Megadeth – "Angry Again"
* Suicidal Tendencies – "Institutionalized"
* White Zombie – "Thunder Kiss '65"
1995 Soundgarden United States Spoonman
* Anthrax and Public Enemy "Bring the Noise"
* Megadeth – "99 Ways to Die"
* Pantera – "I'm Broken"
* Rollins Band – "Liar"
1996 Nine Inch Nails United States Happiness in Slavery
* Gwar – "S.F.W."
* Megadeth – "Paranoid"
* Metallica – "For Whom the Bell Tolls" (live)
* White Zombie – "More Human than Human"
1997 Rage Against the Machine United States Tire Me
* Korn – "Shoots and Ladders"
* Pantera – "Suicide Note, Pt. 2"
* White Zombie – "I'm Your Boogieman"
* Rob Zombie and Alice Cooper – "Hands of Death (Burn Baby Burn)"
1998 Tool United States Ænema
* Corrosion of Conformity – "Drowning in a Daydream"
* Korn – "No Place to Hide"
* Megadeth – "Trust"
* Pantera – "Cemetery Gates"
1999 Metallica United States Better than You
* Judas Priest – "Bullet Train"
* Nashville Pussy – "Fried Chicken and Coffee"
* Rage Against the Machine – "No Shelter"
* Rammstein – "Du hast"
2000 Black Sabbath United Kingdom Iron Man
* Ministry – "Bad Blood"
* Motörhead – "Enter Sandman"
* Nine Inch Nails – "Starfuckers, Inc."
* Rob Zombie – "Superbeast"
2001 Deftones United States Elite
* Iron Maiden – "The Wicker Man"
* Marilyn Manson – "Astonishing Panorama of the Endtimes"
* Pantera – "Revolution Is My Name"
* Slipknot – "Wait and Bleed"
2002 Tool United States Schism
* Black Sabbath – "The Wizard"
* Slayer – "Disciple"
* Slipknot – "Left Behind"
* System of a Down – "Chop Suey!"
2003 Korn United States Here to Stay
* P.O.D. – "Portrait"
* Slipknot – "My Plague"
* Stone Sour – "Get Inside"
* Rob Zombie – "Never Gonna Stop (The Red Red Kroovy)"
2004 Metallica United States St. Anger
* Korn – "Did My Time"
* Marilyn Manson – "Mobscene"
* Spineshank – "Smothered"
* Stone Sour – "Inhale"
2005 Motörhead United Kingdom Whiplash
* Cradle of Filth – "Nymphetamine Fix"
* Hatebreed – "Live for This"
* Killswitch Engage – "The End of Heartache"
* Slipknot – "Vermilion, Pt. 1"
2006 Slipknot United States Before I Forget
* Ministry – "The Great Satan"
* Mudvayne – "Determined"
* Rammstein – "Mein Teil"
* Shadows Fall – "What Drives the Weak"
2007 Slayer United States Eyes of the Insane
* Lamb of God – "Redneck"
* Mastodon – "Colony of Birchmen"
* Ministry – "Lieslieslies"
* Stone Sour – "30/30-150"
2008 Slayer United States Final Six
* As I Lay Dying – "Nothing Left"
* King Diamond – "Never Ending Hill"
* Machine Head – "Aesthetics of Hate"
* Shadows Fall – "Redemption"
2009 Metallica United States My Apocalypse
* DragonForce – "Heroes of Our Time"
* Judas Priest – "Nostradamus"
* Ministry – "Under My Thumb"
* Slipknot – "Psychosocial"
2010 Judas Priest United Kingdom Dissident Aggressor
* Lamb of God – "Set to Fail"
* Megadeth – "Head Crusher"
* Ministry – "Señor Peligro"
* Slayer – "Hate Worldwide"