Cool thread.
Anything that's not too ambient, unless I'm about to do a challenging set. I've listened to too much Cruise-Asceticists-era WH during strength training it's ridiculous. Con-Dom's material on War Against Society does the job. Grunt and Deathpile are nice, too. S.T.A.B. electronics is also a consistent go-to. Anything self-loathing and miserable also works for me in a strange way, Even though I don't feel that way at all.
I recently got water-resistant headphones since it's cutting season and I'll be swimming for cardio on my rest days, the pool area is nearly silent aside from people splashing and the jets from the hot tub. Lussuria, Croatian Amor and the quieter side of the Posh roster, early Lust For Youth, Kassel Jaeger and Jacob Kirkegaard suit this mood nicely.