Where do most of you find music for your projects?

Hey, I'm Jaëxx. I'd like to know where most of you source music you've used in films? I ask because I'm a recording artist and producer (not a film maker like most of you) and I'd like to hear your experiences sourcing music. Films, commercials, internet videos, etc. I don't know any film makers personally, I figured you all would be a good group to ask.