IK Multimedia iRig Midi for iPhone/iPod touch/iPad: Musical Instruments. Alesis iO DOCK Docking Station: Electronics.
Opensoundcontrol.org. MIDI Manufacturers Assocation. TouchOSC. Audeonic (MIDI) MidiVision. Midi Touch. Is a full featured, customizable MIDI controller. It can connect to hardware using the USB Camera Connection Kit , and transmit/receive over MIDI over WiFi. It is compatible with the excellent DSMidiWifi for Mac & PC, and also compatible with a native OS X protocol called for even less latency.
Use the simple toolbar and drag and drop to create a custom controller for each situation.