Create Digital Music has put together an interesting video detailing the various ways that you can connect MIDI gear (synthesizers / keyboards) to your iPad. MIDI (musical instrument digital interface) is the standard means by which musical information is communicated between MIDI capable hardware and software. As Create Digital Music puts it, "... [MIDI] doesn't transmit sound, but it does transmit information like pitch, note events, knob twists, button presses, and clock and transport information."
Using various MIDI-compatible apps on your iPad, and the Apple Camera Connection Kit or the Line 6 Midi Mobilizer, it's actually pretty straight forward getting MIDI gear (from today, dating all the way back to the 1980s) to work with your iPad.
Since Apple introduced Core MIDI into iOS 4.2 and above, it's easier than ever to get your iPad working with MIDI devices -- and that's what the video after the break demonstrates. If you've found some interesting music apps for your iPad, but you're struggling to integrate them with your music-setup (or even just use a MIDI keyboard with your iPad) then the video after the break is for you.