Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
Coming soonish: AU3FX series
At last, I know some of you have been waiting a very long time for this I'm porting my old AUFX IAA effect apps to AUv3 format. Note that these will be released as new AUv3 apps, not as updates of the old apps. (So don't go buying the IAA versions hoping they will be updated for free to AUv3.)