Vocals tend to pull my focus, and repeated phrasing in a lot of EDM is distracting. I find post-rock as a great genre for coding. I frequent the r/postrock sub-Reddit and keep yearly Spotify playlists updated with new releases [1].
I have also enjoyed combining jazz with a rain simulator like RainyMood [2]. Volume-balance them together and it's sublime.
Wolves in the Throne Room and So Hideous are great examples of metal bands with sweeping atmospheres and non-intrusive vocals.
The Algorithm and Master Boot Record are metal-inspired electronic music with no vocals.
Video game soundtracks also work well. Danny Baronowsky, Ridiculon (The End Is Nigh soundtrack is phenomenal), and Disasterpiece are some of my favorite indie game composers.
Metroid Metal is kinda similar, but it's highly technical prog-metal covers of music from the Metroid series. Descendants of Erdrick and Armcannon are also enjoyable metal video game cover bands.
If you want to get lost in coding for a long while without needing to change albums, Chronicles of Time is a 5 hour long compilation of covers of music from Chrono Trigger by a huge variety of artists. If you listen to this from start to finish without stopping, you should probably take a break and stretch for a while.
I really enjoy the soundtrack from Elder Scrolls Online. The new Doom has an excellent soundtrack as well, though it does have occasional voice-over.
I love listening to video game soundtracks when working.
If I want to focus 100%, work fast and have no idea what’s going around me, I’ll put some fast paced Kirby music from the SNES versions and code away as if I was racing King Dedede.
If I want to get in the mood for some architecting or refactoring, I’ll put some Final Fantasy chip-tunes to work through the mysteries.
The soundtrack for Shovel Knight is also excellent. Even though the game is recent, the music is completely authentic to capabilities of the sound chip in the NES.
That said, I find the sound of the NES to be a bit too bright and crisp for background listening. I agree that SNES era music is easier for programming. Super Metroid, Secret of Mana, Secret of Evermore, Final Fantasy 2 (FFIV in Japan), Final Fantasy 3 (FFVI in Japan), Chrono Trigger, and Earthbound immediately come to mind as great soundtracks.
The music from SNES games is stored in SPC files (individual songs) and RSN files (collection all SPC files for a game). The files are extremely small. You could probably fit the soundtracks for every official SNES game into a few dozen megabytes. You can learn more about the format at the Video Game Music Preservation Foundation wiki: http://www.vgmpf.com/Wiki/index.php/SPC
The London Philharmonic has some great video game cover albums as well.
I've tried listening to metal and it works if the lyrics aren't distracting, but anything I know the lyrics to or any lyrical styles I hate (the grunting or pig noises) really distract me. It's hard to find a good random metal playlist that doesn't have any of those two distracting factors.
Instrumental prog metal is really good for getting work done though.
I've recently discovered post-rock as well and it's perfect. It's so boring that my mind tunes it out, which is what I'm looking for.
I've spent so much time trying to find good electronic music that doesn't have any vocals at all, and it's frustrating. Post-rock is great for letting your subconcious drift away while you work.
Mostly: anything without easily discernible or deep lyrics that distract me. This could be Black Metal, EDM, classical music.
Also ok: Stuff I really like and know really well, e.g. Metal with understandable lyrics, 80s Synthpop, Soundtracks
Usually not ok: ballads, rap, stuff with lyrics in my mother tongue
Special mentions: EVE Online OST: https://soundcloud.com/ccpgames/sets/eve-online-login-screen..., The Cat Empire, Dirty Doering, Pendulum, Massive Attack, Portishead, or random DJ sets