Not many music app sales this weekend so we stretched it out to include the past week or so:
Free

Bugle ($0.99 > Free) - it’s free
iXY MIDI Controller ($0.99 > Free) - get it while it’s free!
MIDI Motion Machine ($0.99 > Free) - accelerometer based MIDI controller app

$0.99 and Up

Name That Guitar Riff ($1.99 > $0.99) [...]