Meteor updated with AudioBus support
Meteor is multitrack DAW designed by 4pockets (developers of StompBox so you can expect high quality effects). Audiobus support is a big step forward for Meteor but the app still has problems with user interface and terrible implementation of midi tracks and virtual instruments. I can recommend to use this only for audio recording.
Synergy Studio (from same developers - 4pockets) price drop
Orphion - unique musical instrument for iPad became free. Definitely worth trying.