DIY Sensor Film Kit - 4x6" Small Kit is a great new way to make custom-sized sensors out of force sensitive material. This kit includes one piece of black plastic sensor film (it's thicker and more durable than Velostat but similar in function), two pieces of heavy aluminum foil, and two pieces of clear adhesive polyester film. The sensor film is super durable and changes its electrical resistance when force is applied. It's a lot like Velostat but a bit more responsive. The aluminum foil is for electrodes and the clear adhesive polyester film is given to keep the sensors together. It's a great way to make a FSR of any size for your microcontroller project.
There's more info on the DIY Sensor Film Kit - 4x6" Small Kit site including easy instructions on how to make a basic sensor. They also have a bunch of examples of what you can do with the kit.
Sensor Film Kit Site: http://www.sensorfilmkit.com
Adafruit Web Site: http://www.adafruit.com/products/1917