Metronaut - An app to help you play classical music
Audio Hero - Over 250,000 royalty free music & sound effects for videos
Transposr - A free and simple way to transpose your sheet music or MP3.
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!
Flat for Education - The best way to teach music to your students
Free Music Archive - Interactive library of high-quality, legal audio downloads