Dave Holmes lists dozens of both obscure and well-known podsafe music resources at Dave’s Imaginary Sound Space.

Unfortunately it becomes extremely time consuming for podcasters to source available music and listen to it.

…

The sites I refer to here represent a tiny fraction but even so it’s clear to see the potential pool of music podcasters can draw from. It shows there’s a strong cultural movement that is rapidly taking advantage of new media technologies and confirms podcasting’s role as an important music delivery component.

Time consuming? Yeah — you could say that. I have been through over 4000 tracks over the last year. Around ten percent I have kept and only two percent have been given a 4+ rating in iTunes. Via the Creative Commons blog.