Might it be possible to buy another fan to attach to the radiator instead of changing to air cooling? Or is the water pump contributing too much to noise?
Anyway, take a look at this page: http://www.frostytech.com/top5heatsinks.cfm
It's not always as up to date as it could be, but look at some of the low-noise Intel and AMD coolers. Most of them probably come with brackets for your system.. check with your preferred retailer.