There has been other sub categories of doom metal. A few of these variations and styles come from motivation of doom metal and other metal genres. The follow are some of the more common sub genres of doom metal.

Traditional

Most if not all of doom metal started here. With doom metal starting in the 90′s most bands today still belong to this sub category. Doom metal that has heavy distortion along with a slower tempo with heavy distortion is usually falls within the Traditional sub genre. You will discover plenty of clean vocals, with some high pitched screaming. Traditional bands include Witchcraft, Reverend Bizarre and Ogre.

Epic Metal

Epic is very close to Traditional metal. The style of vocals is what changes the two. There is cleaner singing in Epic metal.
Bands that belong to this group are Solstice, Doomsword, Candlemass and Solitude Aeturnus.

Stoner Doom Metal

Stoner is generally known as Psychedelic Doom Metal. Why you might ask, because it has psychedelic styles on the music. Watch for a lot of effects with synthesizers and guitar pedals when listening to this style of music. Their music usually includes guitar effects like phaser, fuzz and flanger. Stoner bands were the initial artists to use guitar pedals and effects. Consider bands like Acid King, Sleep, Sons of Otis, Electric Wizard and Kyuss for more stoner metal.

Doom Metal – Sludge

If you put metal, hardcore punk and southern rock in one you get sludge metal. These bands emphasize more of a fast tempo within their music. With guitars using a sluggish sound and the drum kits using double bass to form fast beats, this isn’t typical for doom metal bands. Singing about politics, drugs and society provides you with a concept on what Sludge metal is all about.
For more information on Sludge metal consider these bands: Eyehategod, Crowbar, Acid Bath and Grief.

Death

Putting together some really heavy distortion and slow tempos provides you with more of a death metal feel. The vocal style is the largest change in this sub genre. Snarls and growling are the most frequent ones. Death Doom metal has more double bass pedal drumming as opposed to typical doom metal style. Most bands that fall into this category were influenced by Celtic Frost and Hellhammer. Take a look at bands like My Dying Bride, Asphyx, Paradise Lost, Autopsy and Winter.

Black Doom Metal

This sub genre is known as Black or Blackened Doom metal and it combines the features of black and doom metal. The vocals will have a high pitched scream and their guitars have a great deal of distortion. Black metal has a slower tempo, while having their music filled with distortion.
Have a look at Gallhammer, Nortt, Dolorian and Ajattara for more info.

Doom Metal will Always Be Around

The above mentioned of a few of the other sub groups of doom metal. There are even more than these. It started in 90′s and rising today. Doom metal will carry on and produce new songs and bands as the world continues on.