Check out the Aurora, an open source DJ Mixer created by the trio of Matt Aldrich, Mike Garbus, & Maro Sciacchitano. This USB powered device features two linear channel faders a single a/b crossfader, eight back lit buttons and twenty four back lit knobs which allow one to control effects. This wonderful, little mixer easily integrates with your favorite midi compatible software, no problem there!

Really good with wiring? The Aurora team provides a list of everything you will need to make one for yourself, if you know that route. Post your ideas or modifications in the Aurora forum and keep it a communal thing that we can all share solutions about.