Jim, I use the iRig Pro, which has both audio and MIDI input (but not output) to the iPad. That, in conjunction with the KMI MIDI Expander gets me hooked up to my KMI SoftStep.

If you want a Bluetooth connection you could either wait for the BT-4 from Positive Grid - and who knows when that will be released - or you could go for the IK Multimedia BlueBoard, which I have as a backup. Sometimes my guitarist uses it with my backup iPad as well. It works well, the connection seems stable. One of the nice features the BlueBoard offers - two 1/4" inputs for foot controllers (volume, gain, wah, whatever).