It depends on what you mean by "chords used." In "Ea Lord or the Deep" intro Mister Varg arpeggiates through a simple Cminor and then a Bminor followed by some Cmin noodling. The keyboards in "Det Som Engang Var" add upper register notes to the power chord sequence of the guitar (E5, F#5, G5, A5 IIRC) that spell out some odd chords. Gorgoroth use some minor 6th notes with power chords (watch the Black Mass Krakowa video to see)... Im pretty sure that they are not alone in metal in doing this; a power chord on the A string invites one to add the sixth note (or a fifth, which is also common) on the low E string. "Transylvanian Hunger" main riff suggests A5, Amin, Asus2(or add9, can't remember how that rule works...) and on the slow breakdown there are several times where an Eminor is played. Rob Darken uses the inverted power chord quite a bit ("Battle of Wotan's Wolves" main riff uses it quite distinctively) where the fifth note rather than the tonic is the lowest note played. You might want to look into some of his more recent work, the guitars seem to be playing some more chords with some upper extensions, but its hard for me to tell because they are always mixed so far back. Gorath sounds like they use some unusual chords. There are doubtlessly many other bands and songs that use chords besides the 5th chord... black metal seems to like the flat 2nd, flat 3rd, flat 5, and natural 7th sound quite a bit in writing melodies/leads, and it would not suprise me in the least to see those notes turn up as harmony in chords.