Bought this a while ago on a whim, and have hardly used it. It's Uncle Uli's take on the Alesis ioDock. It adds all of the I/O that you want for music making: * Mic/Line/guitar inputs * Audio outputs * Headphone output * MIDI In and Out * Footswitches
Important note: this uses the 30-pin connector
It also charges the iPad at the same time (assuming it's plugged into the mains), but can be used with batteries for mobile music making.