I was not a huge fan of the music that came out this past year. Very blah. I didn't get into a lot of the new metal that's out there.
Here are my favorites from 2004.

Lamb of God
Ashes of the Wake

Released August 31, 2004
http://www.lamb-of-god.com
Shadows Fall
War Within

Released September 21, 2004
http://www.shadowsfallrocks.com/
Twisted Sister
Still Hungry

Released October 19, 2004
http://www.twistedsister.com/
Brides of Destruction
Here Comes the Brides

Released March 9, 2004
http://www.bridesofdestruction.com/
 
Hazen Street
Hazen Street

Released July 20, 2004
http://www.hazenst.com/
Scars of Tomorrow
Rope Tied to the Trigger

Released February 24, 2004
http://www.scarsoftomorrow.net/
 
Premonitions of War
Left in Kowloon

Released January 27, 2004
http://www.premonitionsofwar.com/

 
Madball
N.Y.H.C. EP

Released 2004
http://www.madballnyhc.com/
Vicious Circle
The Art Of Agony

Released November 29, 2004
http://www.viciouscircle.tv/
Crossfade
Crossfade

Released April 13, 2004
http://www.crossfadeonline.com/

 
Breaking Benjamin
We Are Not Alone

Released June 29, 2004
http://hollywoodrecords.go.com/
breakingbenjamin/
Skindred
Babylon

Released August 31, 2004
http://www.skindred.com/
Kelly Clarkson
Breakaway

Released November 30, 2004
http://www.kellyclarksonweb.com/
Arvil Lavigne
Under My Skin

Released May 25, 2004
http://www.avril-lavigne.com/
Ashlee Simpson
Autobiography

Released July 20, 2004
http://www.ashleesimpsonmusic.com/