Game Center - Game Center brings social gaming to OS X and iOS apps.
Music For Makers - Licensing good music has never been this easy.
GameStreamer - Connection people and games anywhere.
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!
OpenGameArt.org - A site dedicated to sharing artwork & other assets for game development.
AIVA - The AI composing emotional soundtrack music