Yes, they are extremely different bands. Dark Angel is like Slayer except twice as Slayeresque (if that makes sense).
Okay, here's a list to keep you occupied...most of this stuff should be on SoulSeek.
Annihilator: Alison Hell, Epic of War
Anthrax: Belly of the Beast, Metal Thrashing Mad, Armed And Dangerous, AIR (their less known shit)
Dark Angel: Darkness Descends, Merciless Death, An Ancient Inherited Shame
Deströyer 666: Black City - Black Fire, I Am the Wargod, Raped, Unchain the Wolves, Australian And Antichrist (black/thrash from HELL...everyone must hear this band)
Destruction - Thash Till Death, Nailed To the Cross
Forbidden - Chalice of Blood, Infinite, Forbidden Evil
Heathen - Pray For Death, Opiate of the Masses (a bunch of shit is available at
their site.
Imagika - Fade Away
Kreator - Material World Paranoia, Tormentor, Toxic Trace, Coma of Souls, Awakening of the Gods
Nuclear Assault - Cross of Iron
Overkill - Gasoline Dream, Nice Day...For A Funeral, Elimination (good call, Matt), Deny the Cross, Feel the Fire, What I'm Missin', E.Vil N.Ever D.Ies, Live Young Die Free, oh so many more....
Sadus - The Wake, Oracle of Obmission
Sodom - Baptism of Fire, Nuclear Winter, Sodomized, Remember the Fallen
Toxic Holocaust - War Is Hell, Evil Never Dies
Ulysses Siren - Terrorist Attack, No Trace of Shame (most underrated thrash band ever)
Vio-Lence: Calling In the Coroner, I Profit (takes a while to get used to the vox)
More if I can think of any.