Think that the keytar isn’t geeky enough for you?
Then you may want to build a DIY Kaossilator Guitar.
James Haskin came up with the idea for this project after seeing a video of Wayne Coyne of The Flaming Lips. He had mounted his Kaossilator on a guitar and a taped the neck of a video game controller next to it to make it look like he was fingering the notes.
Instructions for building the Kaossilator Guitar Synth are available at Instructables.