Hey BeepBoy. I'm triggering transistors with the arduino that are connected to/triggering three keyboards and 2 little $5 samplers (the black boxes). 
Here are some schematics:
http://casperelectronics.com/finished-pieces/circuit-bending-tutorial/interfacing-with-the-arduino/

The two Casio SK1s have sequencers in them that record what I am playing. The arduino is triggering the "one-key playback" feature of the sequencer. 
The other keyboard provides the drum sounds.
The two samplers are picking up the sound from the room. They are randomly triggered to record and playback.