This is the first water cooling system I saw that would not scare me away to install in my PC. The Water Cowboy from Japanese Digital Cowboy is a 450W ATX power supply with integrated water cooler for CPUs.

The design reduces the complexity of a water cooling system quite a bit. Two water pipes come out of the ATX power supply and connect to a cooling device that is placed on the CPU (LGA775 and Socket 754/939 are supported) and this is it. The power supply fan cools the air and the integrated water radiator.
Check out this hi-res photo to see how clean and neat this system installs inside an ATX case.

I could not find any information on the availability of Digital Cowboy products outside of Japan.
The Water Cowboy will be released in June in Japan.
More details on Digital Cowboy (Japanese). Via PC Impress Watch (Japanese).