You may have already heard of it, but I just discovered it by accident. CHDK. This is alternative firmware (overlays in RAM, so doesn't change the camera permanently) for many Canon cameras, including my Powershot AS100 IS, that provides many features not included in cheap cameras, like saving in DNG raw, manual/overide, histogram display, DOF calculator and even more - such as scripting.
I have just now been able to get it working in mine, even though the version for my camera is only at alpha development. It makes my cheap P&S so much more powerful - for free!