A new VirtualMIDI app has arrived for iPhone. ChordMapMIDI offers a simple screen for quickly trying out different chord progressions, on anything you're sending MIDI at... well, anything that is polyphonic!
Although the graphic design is appalling, the actual layout looks well thought out. It could be a lot of fun to plug this into one of the Guitarish Animoog patches, and then bring up the Music Theory Cheat Sheet on your computer.
On a total tangent: while researching this I came across an interesting article by Anthony over on the Ableton Cookbook, Music Theory for Electronic Music? Don't waste your time. I'm in total agreement, and this is one of the reasons I try to avoid theory in ECPM. It seemed like the more I learned about theory the more stale my music got. Intervals and Chords are about all you really need to know, and with apps like this you don't even need to know those either!