Just read an intersting article in the current issue of Sound on Sound (doesn't seem to be available online, but here's a similar one) about the Rainboard, a forthcoming MIDI controller from Brett Park.
Rather than the usual layout of piano keys, rectangular rows of buttons or the like, the Rainboard offers a clustered grouping of controls I find really interesting. As the relationships between keys are completely programmable according to whatever parameters are desired, the potential to develop and cultivate intuitive note relationships is compelling indeed.
Here's a short video where Park demonstrates the Rainboard:
And here's a performance video: