You're all forgetting one important, rare genre:
Volbeat Metal
Volbeat is a metal band from Denmark who combines the unique stylings of Metallica, Social Distortion, Johnny Cash and Elvis into one unique, rare expression of metal. It's like an unusual twist of heavy metal, classic rock-n-roll and rockabilly. Their music, alone, is a genre all their own. Singer and guitarist Michael Poulsen had a death metal band prior to starting Volbeat. Said death metal band, Dominus, was his first band, and when he got sick and tired of the death metal music and the death metal scene, he broke up the band.
The styles he incorporates into each song is unique and never truly the same in each song. Michael is very talented--he writes all the music, makes the guitar riffs and what have you. He's a huge Elvis and Johnny Cash fan and uses them as big influences as seen in songs like "Sad Man's Tongue" or "Soulweeper" and "Soulweeper, Pt. 2". I highly recommend listening to Volbeat if you're looking for something DIFFERENT than the usual metal genres.
XDD Lol, just so everyone knows, I'm joking about them having their own genre. I just really love Volbeat and felt the need to SHOW IT OFF. Because they really are different in comparison to other metal bands. I'm really not sure WHERE they fit in the sub-genres of metal.