So far I have found:
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200answers:
6I've used Podsafe Audio in the past for music from independent artists who are perfectly happy for you to use their music in your projects.
Freesound provides an excellent, searchable database. It also has a convenient little "player" built in so you can hear the samples before you buy.
The Freesound Project is a collaborative database of Creative Commons licensed sounds. Freesound focusses only on sound, not songs. This is what sets freesound apart from other splendid libraries like ccMixter. New to this site? Read the What is Freesound page to learn more!
SoundDogs have a ton of sounds, but it's often hard to find good ones there are so many, and not specifically geared towards applications, but I've used them before. Looking forward to checking out some of the other suggestions here.