"Explore 44,500 selected recordings of music, spoken word, and human and natural environments" from the British Library collection. If you're outside the UK, copyright limits this to 22,500 items. Still, some great recordings here.
"ccMixter is a community music site featuring remixes licensed under Creative Commons where you can listen to, sample, mash-up, or interact with music in whatever way you want.
Remixers If you're into sampling, remixing and mash-ups grab the sample packs and a cappellas for download and you can upload your version back into ccMixter, for others to enjoy and re-sample. All legal."