Top 10 Debut Albums

Life of Agony - River Runs Red
Exodus - Bonded by Blood
Skyclad - wayward sons of mother earth
Hell - Human Remains
Celtic Frost - To Mega Therion
Skid Row - S/T
Wildhearts - Earth vs.
Carcass - Reek of Putrefaction
Alice in Chains - Facelift
Testament - The Legacy
 
I agree with a lot of the albums already listed. Good to see Van Halen's debut album get mentioned. Here are a couple that I think people have overlooked:

Rage Against the Machine - RATM

Death Angel - The Ultra Violence - This band is under rated by a lot of thrashers. It is an incredible album, even more so when you consider how young they were when they created this masterpiece.

Korn - Korn - Haters are going to hate, but this is a fun album and it served as a gateway band to heavier music for me and I am sure many others of my generation. If nothing else, it was a welcome change from grunge. I like this album and this band more today than I did when it was first released.
 
Zero's mention of Korn reminded me of Mudvayne's first album, L.D.50. Don't really know about people's views on that album but I quite enjoy it.
 
Down - Nola
Cynic - Focus
Emperor - In the Nightside Eclipse
Mayhem - De Mysteriis Dom Sathanas
Morbid Angel - Altars of Madness
Candlemass - Epicus Doomicus Metallicus
Ozzy Osbourne - Blizzard of Oz
Entombed - Left Hand Path
Metallica - Kill 'Em All
Death - Scream Bloody Gore
 
You know what, it's almost kind of like a demo version of Citizen Brain. I for one really enjoy it, it depends - if you like polished production then you'll hate it, it's a bit demo-y.
 
Darkthrone - A Blaze in the Northern Sky

I hate to be that guy, but A Blaze in the Northern Sky wasn't their debut. Soulside Journey was... though in a sense I wouldn't argue with you, A Blaze in the Northern Sky was such a massive shift in sound (probably the biggest shift in sound between albums there has ever been) they might as well be different bands!

For anyone who doesn't know what I'm talking about, before Darkthrone became one of the most important and influential black metal acts they put out Soulside Journey (a death metal album in the vein of the classic old school Swedish bands such as Entombed, Dismember etc.)
 
I hate to be that guy, but A Blaze in the Northern Sky wasn't their debut. Soulside Journey was... though in a sense I wouldn't argue with you, A Blaze in the Northern Sky was such a massive shift in sound (probably the biggest shift in sound between albums there has ever been) they might as well be different bands!

For anyone who doesn't know what I'm talking about, before Darkthrone became one of the most important and influential black metal acts they put out Soulside Journey (a death metal album in the vein of the classic old school Swedish bands such as Entombed, Dismember etc.)

Damn, how many metulz points did I just lose?