While there have been some MIDI solutions out there for the iPad and other iOS devices, Yamaha has introduced (PDF) its first MIDI interface for iOS at the Frankfurt Musicfair.
In a small, black device the i-MX1 carries the needed electronics and two connectors for the included adapter cables which represent the MIDI input and ouput (with the well known 16 MIDI channels each). It does not just connect to the iPad, but to the iPhone and the iPod Touch, too. Since these devices are much smaller, they are even more handy controllers.
The i-MX1 is compatible to the drivers provided by the iPad-OS (iOS, Core MIDI), theres no need for special drivers. So even third- party applications that are using the iOS drivers can use the i-MX1 as MIDI-Interface.