In some sort of order.

Jamendo

Free Music Archive (FMA)

ArgoFox (on YT)

NoCopyrightSounds(on YT)

Musopen(classical PD music)

Dusted Wax Kingdom

–//–

And older:

Grunfeld DML (Deep House)

Ideology.de

Thinner netlabel

CyberCrunk records(CCK Drum&Bass)(on SoundCloud)

Hornet and Scene.org archives

LePork records

LibreMusicWiki page(RIP)

Here’s a couple I’ve seen around, tho I haven’t dived too deep:

• OpenGameArt (Usually kind of a mixed bag on quality, but the site has good concept and intentions)
• https://musopen.org/ (public domain, classical stuff, also a bunch of sheet music if you want to do things the hard way)
• https://degitx.com/ (an individual that produces rock/metal/chiptune kinda stuff and puts it out under CC licenses)
• https://gravitysound.studio/ (Had it bookmarked, but it seems the free page is gone or at least moved. Looks pricey, and terms don’t seem clear)

Edit: deleted

Never mind. Misunderstood the question.