I notice several visitors have been to the posts where I talk about my cheap one-button MIDI devices. I currently make them with Arduino, which is these days pretty much a no-brainer (one resistor, and the MIDI library already packaged in the IDE.) I've been working on doing them both by bit-banging one of the cheap thru-hole AVRs (aka ATtiny45), and by leveraging TeensyUSB or a similar USB-AVR breakout board to send MIDI over USB. There is also a new solution based around the latest crop of Arduino's that makes use of the fact that the Uno uses an AVR (ATMega8U2) instead of the older FTDI chip for USB.
Anyhow. I'd gladly document, or even make an Instructable, on my cheap MIDI solutions if I thought there was sufficient interest. Someone answer this post, and we'll see.