http://www.quietpc.com/uk/watercooling.php
Opinions? Can only find one review, plus someone on [H] forums who has one. Says it gets about 45c under full load at 2.2GHz which is about the same as SLK800/900 but totally silent, this was also with no other fans running in the PC.
Externally powered which is a little worrying (wouldn't want to forget to turn it on).
Downside, little pricey and it's on the large side.
David, *cough* get one for review :D