We expect many Lightning-enabled accessories to be coming from companies at CES 2013. Griffin today announced an update to their StudioConnect Audio/MIDI dock which adds a Lightning connector. They claim it to be the first music creation accessory that supports the Lightning connector.
StudioConnect gives your iPad: audio in and out, MIDI in and out, and a stereo headphone jack with its own volume control so you can monitor what's going in (or out).
The StudioConnect with Lightning will be available in the Spring of 2013 and will cost $149.