I'm sure this question has arisen in the minds of those set on creating their own sonically destructive, electric transcendental ditties.
The technological world is overwhelming. Ultimately, what one needs for recording a piece of music isn't much at all. You could employ the worst of equipment as a means to an aesthetic end and in this sense, it's easy to discard the idea of rig having any significant importance to the overall product (especially from an underground perspective, which often tends to favor content over presentation). However, metal has posed various problems for musicians, producers and venues who need to get the best clarity and representation of the artist as they intend. While one could certainly get away with poor equipment given proper production techniques and mic'ing methods, getting away with such a poor setup in a live setting proves elusive. Thus, acquiring half-decent gear is simply inevitable if one wants any sort of clarity and adequate tone to match their aesthetic needs. This seems to reinforce the idea that while presentation, specifically from a production standpoint, is secondary, that it's still important to thoroughly consider from a holistic perspective. Essentially, overlooking this critical component would be like settling with little to no clarity (ie garage quality) or with overproduced and inorganic renditions (ie. clicky bass drums a la Decapitated/Dimmu Borgir) which are aesthetically incompatible with the thematic aura of the song at hand.
I've come across many bands which serve as headbanging fodder in a live setting, if only because venues and sound crew are unable to (or don't care enough) allow the guitar to come to the forefront so that a band can showcase their riffs. This is besides the fact that most metal, especially in a local setting, doesn't operate with "riffs" in mind, but rather derivative power chord forms shifting aimlessly in the low end registers. However, it is once again inevitable to notice that the difference between good and bad gear is like night and day. In this light, I think it makes sense to unload a relatively impressive sum of money as an investment in one's sonic and thematic end.
I am a guitarist mainly and so am thinking in terms of guitars, pickups, amps (head/cab) and possibly pedals.
Amps I have found to be adequate for achieving a chunky sound:
Marshall JCM Heads. JCM800/900 are considered some of the best and most sought after tube amps. However, the DSL 50/100 is a great tube amp which has your essential 2 channels and a great classic distortion that is sure to please anyone vying for solid, clear and consistent black metal tone. Alternatively, the tone is great for any other tones for other genres. The downside is that this can run a 1000+ dollar gorge into your pockets. This is what I currently own at the moment and I'm happy with its sound.
Mesa Dual Rectifier Heads (or Mesa Heads in general really). Very beefy and handles low end incredibly well. Ideal for high gain, high output material. Ie. ideal for metal. Downside is that they can run 2k++
Mesa Cabs likewise are able to handle the chunky low end that arises from a need of "fullness" from one's tone. Downside is once again another k dropped into your rig.
Now, I think that guitars simply come as preference and a matter of comfort, but Ibanez RG's have long been the choice of badarsery. I have myself a fairly low end Iby 7-string RG that works wonders. The stock pickups work well. I also have a 6-string RG Prestige into which I dumped considerable money into. Here's a tip: if you're consistently changing tunings and don't like to play the whammy like you're Kerry King, Floyd Rose is a useless system. However, the RG Prestige line is really well-made and utilized a very thin neck that's conducive to the healthy development of chop-intensive metal playing. Speed and conciseness in one package.
Jazz III picks. All day.
DiMarzio house a wide array of great tonally varied sounds. I tried their X2N, the most high output pickup and it's ridiculously trebly and intense, perhaps great for black metal. Otherwise their tone zone and paf pro give excellent clarity.
At the end of the day though, the head/cab seem most important. Invest in a decent tube head and a cab and you're set. Thoughts? Other's preferences? Cheap alternatives?