I'm looking for a silent (preferably fanless) heatsink for my X600 pro graphics card. The current fan sounds like a wind turbine, so anything would be an improvement.
Here's something promising from Zalman on the epcbuyer site:
Zalman Silent Graphics Card Heatsink with Heatpipe (ZM80C-HP) for £16 inc VAT.
Also the Zalman ZM80D-HP from QuietPC for £27 inc VAT.
Komplett.co.uk sells this Zalman Passive Heatpipe VGA Cooler for £19 inc VAT.
C&C Central sells the ZM80C for £20 and the ZM-80D for £23 inc VAT.