My previous attempt at a Morse code keyboard worked over USB and used a copper coin as a capacitive sensor. Since then I've acquired a real telegraph key and Adafruit's Bluefruit EZ-Key board. With that and a Trinket I made a Morse code Bluetooth keyboard. It works with any computer that has Bluetooth (also phones and tablets).
Here's what it looks like in action (as usual please excuse my lack of Morse code skills):
Here's the Arduino sketch that's running on the Trinket. As before there's a buzzer for feedback and the transmission speed is fixed.
If you're into Morse code, I continue to recommend my Android application that listens to Morse code using your smartphone's microphone and translates it to text.
Here's a diagram of the connections: