For my deep sky imaging efforts I bought a 40D which I sent to Central DS in Korea to be modded. The modification is in two parts. The first part is the removal of the Canon front sensor filter. This is replaced with a spectrum enhanced UV/IR filter. This filter allows the precious Ha light to pass through and hit the sensor. It also means that you don't end up with blue nebulae unless it really is blue. The downside is that unless you have a specialised front filter to clip over your lens or mirror box; the camera cannot be used in daylight hours.

The second part to the modification is the cooling system. This is a TEC peltier finger plate that applies sub zero temperatures to the sensor. Sensors get very hot when left on in bulb mode for long periods of time. That results in lots of noise and effectively means that you cannot really run an uncooled camera for any longer than 10 minutes. With the modification that Central DS do you can run your camera in bulb mode for 40 minutes or more. Noise is just not an issue. It also means that darks are no longer really necessary.

Lastly this is far cheaper than buying a dedicated cooled astro camera.