For root + perfect fourth, "Forgotten Centuries" by Emperor (first chord in the riff that alternates between lead and chord/rhythm playing about half-way though the song) is an obvious black metal example. I'm having a hard time coming up with death metal examples, but that's probably because I play much more black metal than death metal. A slightly more esoteric, but more well known example, would be the first chord in "Transilvanian Hunger" by Darkthrone, although the fourth is played an octave high (!)- that first riff also contains examples of root + m3rd, root + M2nd (!), root + m6th, and is one of the few metal riffs that's entirely in one key (A minor).
Also, although you've left them out, root + m6ths are pretty common in black metal- a few examples are "My Journey to the Stars" (riff 2) by Burzum, "Crushing the Scepter" (first fast riff) by Gorgoroth, and almost every song on "Transilvanian Hunger" by Darkthrone (perhaps most prevalent in "Slottet I Det Fjerne").
Also, don't negelect the barre-chord minor traids heard in songs like "De Mysteriis Dom Sathanas" by Mayhem, practically every song on "Under Ein Blodraud Maane" by Manes, and "Thule" by Thorns.