CHDK is free enhanced firmware for your Canon Digic II based point and shoot camera. With the CHDK firmware loaded, your camera will get the following features:

• Shooting in RAW
• Live histogram (RGB, blended, luminance and for each RGB channel)
• Zebra mode (blinking highlights and shadows)

More info on how the CHDK Firmware Makes Ordinary Canon Digital Cameras Run on Steroids at Shutter Box Philippines.