If you've missed this new controller from Keith McMillen you should definitely see this video of QuNexus.
Of course it is not the first mobile keyboard on the market but it comes with really nice features like areggiator and vibrato.
Classic piano-like keyboards are limiting for electronic instruments and QuNexus pushes the limits of MIDI controllers.
"QuNexus senses pressure, velocity and tilt, which makes software synths come alive, and let's keyboardists play notes more like a guitarist or horn player. And, it pairs very well with iPad apps like like Animoog, Sunrizer and Magellan.
We think it will be big among hobbyist musicians and prosumers, and it's also great with music learning apps like Synthesia, Piano Legend and Symphonix Evolution."