Ccmixter.org have a ton. Also soundcloud. Aside that the usual ways like Youtube.Also keep an eye for remix contests. Plenty of good vocals from a few well know projects/bands for free ,a chance to get featured and earn some $ or other prizes. Source: over 1 year ago

Find some fitting music to use in your videos. Source: almost 2 years ago

Creative commons remix community (some are non-commercial): ccmixter.org/. Source: almost 2 years ago

For Free and non-copyrighted samples: CCmixter and Freesound. Lots of good stuff there. Source: about 2 years ago

Http://ccmixter.org/ tons of music with a variety of creative commons licenses. Source: about 3 years ago

I used to use soundsnap.com for a lot of things. Source: over 1 year ago

This project took me about 3 weeks of free time. I primarily used Studio One 5 pro for my DAW, and the East West Hollywood orchestra for most of the music. Foley recordings for the sound effects came from soundsnap.com. Source: about 2 years ago

In addition to the previously mentioned soundly, you can also try soundsnap.com. It has a subscription model that is unlimited downloads for a year, if I remember right. But that could be useful as a beginner as well. It doesn't have a fancy UI/library management tool like Soundly, but still worth looking at. Source: over 2 years ago