SImilar to methods used for touch-drum projects.

Quoted: Sew together conductive fabric and anti-static plastic to make your own fabric pressure sensor!

Literally fantastic.

Quoted: ROYAL DEVICE are audiophile quality speaker systems,the BIGGEST SPEAKER of the WORLD and The biggest Horn SUBWOOFER of the WORLD for GREATEST AUDIO ROOM of the WORLD, Featuring new, superb design and outstanding performances, built with the best materials, custom components and drivers, precious wood and state-of-the-art finishing

Oscilloscope, spectrum analyzer, FM AF signal generator, AF noise generator

More free sounds: huge DB

Quoted: Freesound: collaborative database of creative-commons licensed sound for musicians and sound lovers. Have you freed your sound today?

Nice

A nice set of emulators ready to play with, no commitment (no saving your patches, but...) fun nontheless.

Nice set of texts on basic sound construction offered free online.

Can be used anywhere, not just OLPC