Audio Hero - Over 250,000 royalty free music & sound effects for videos
LabChirp - Create simple sound effects on Windows.
TunePocket - Download 11,000+ royalty free music tracks and sound FX. Buy once, use forever. New music added daily. Save over 50% compared to most popular similar services. Incredible value!
bfxr - An online chiptune sound generator.
Strikefree Music - 5 free unique, royalty-free tracks for your videos / week
sfxia - Free retro style sound generator for games.