There are quite a few Arduino-compatible boards floating around on Kickstarter, but here's a really novel idea. The Touch Board is an Arduino-compatible board that has 12 electrodes along one edge. Simply press your finger on one and the Touch Board will react. The Touch Board has an onboard MP3 player, so you have instant touch to sound!
Now here's the sweet bit... You can connect anything conductive to these electrodes so you can turn almost anything into a sensor. Bare Conductive, the makers, specialise in conductive paint (electric paint), so you can use this paint to draw your own sensors. You could draw your own piano, and the Touch board will play a note through the audio jack or convert the note to MIDI!
The Touch Board not only does touch sensing, but can do distance sensing up to 20cm too.
The layout of the Touch Board is the same as the Arduino, meaning you can solder on some headers, and attach an existing shield to the Touch board. Some of the projects Bare Conductive have made are wireless doorbells, an actual bell and a painted-on-the-wall lightswitch.
The Touch Board is so freaking cool, and at £45 it's a steal. You can order yours now via Kickstarter, and also head over there to read more. It's been live 3 days and already smashed its target, which is a testament to just what a novel idea it is.
EDIT:
You can order the Touch Board directly from their website for £55.