Have you ever wanted to hook up a MIDI keyboard to your iPad and jam out in style with Garage Band? It's actually rather easy to connect a MIDI controller to your iPad, but you will need an adapter to let you funnel that MIDI signal into your tablet. Luckily, there a couple of not-so-expensive options.
The camera connection kit is an adapter that essentially turns the 30-pin connector into a USB port, which allows you to plug in MIDI devices via the USB. It's important to plug the MIDI controller into the camara connection kit first and then plug the adapter into the iPad, which avoids a bug that can sometimes pop up wherein the iPad doesn't recognize the device. This solution is great for those simply trying to create a simple MIDI connection.
Note: Because the iPad may not output enough power for your MIDI controller, you may need to connect your controller to a USB hub and the hub to the iPad via the camera connection kit.
2. iRig MIDI
The iRig MIDI adapter provides MIDI in, out and thru using the standard MIDI interface. This gives it a little bit more versatility compared to using the camera connection adapter. iRig MIDI also has a USB port, so you can keep your iPad's battery from draining down while you play. This is great if you are going to use the iPad in a studio or performance environment, or if you are fond of long practice sessions. The versatility does come with a price, though, as the iRig MIDI is significantly more expensive than the camera connection kit.
Sitting between the camera connection kit and the iRig MIDI is Line 6's MIDI Mobilizer II. While less expensive than the iRig MIDI, it doesn't offer the MIDI thru or the USB connection for keeping your iPad charged. But it's a little cheaper than the iRig MIDI.