Recommendations for inter-app audio apps for GarageBand?
From WTF Is Inter-App Audio Apps?

Here’s a list of the apps that currently work with Inter-App Audio in Garageband:

Alchemy mobile
Amplitube (iPhone and iPad, paid and free versions)
Magellan
Nave
Yamaha TNR-i
Yamaha Mobile Sequencer
Yamaha Synth Arp &amp; Drum Pad
AUFX:Space
NLogSynth Pro
iMini
Galileo Organ