Roli's £147 Lumi is a single-octave, semi-weighted bluetooth keyboard where each key lights up as it is played. A simple idea, perfectly executed, useful for learning, demonstrating and showing off with. There's a companion app with lessons, hundreds of demo songs, and it comes with a carrying kit.
Here's a video of Andrew Huang using the Lumi to illustrate the overuse of repeated supertonic notes in contemporary pop music. Roli's accepting preorders at Kickstarter and its website; it ships for Christmas.