As an Arduino can easily interface with computers via the MIDI digital interface, it stands to reason that you can also make all sorts of instruments to create music with, to be captured on a PC for further editing. Although there are plenty of simple drums and guitars out there, an the Laser Harp by Instructables user Pushan Panda is a great example. It uses a stepper motor to rotate a mirror which reflects a laser beam, and each position of the mirror represents a different "string" for the hap. When the laser beam is broken, it is detected by a light sensor and sent back to the PC.
This is another example of a project which may look incredibly difficult, but with some thought can be completed without too much effort. For more information and details on the laser harp, check out Pushan's project page. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
If you're looking into starting with Arduino and motor control - check out our new HBRIDGE: DC/stepper motor shield. Based around the powerful Allegro A4954 H-bridge driver IC you can control two DC motors with complete ease, or one bipolar stepper motor. With connections for external power management, a complete beginners' guide and documentation - motor control couldn't be any easier. For more information and to order, visit the HBRIDGE: page.