Noctua is a company that offers heatpipe based coolers. They are not cheap, but offer the most silent and best performing products available in the market. I really like their products, very impressive, check them out.
Noctua released four new CPU coolers for Intel Xeon and AMD Opteron processors. Optimized for use in dual socket systems, the new DX (Dual Xeon) and DO (Dual Opteron) versions of Noctua's highly successful NH-U12 and NH-U9 series introduce the premium quality quiet cooling performance that has become synonymous with Noctua to the world of professional workstations and servers.
"Maximum cooling performance at minimum noise levels and excellent reliability can be particularly important when it comes to high-end workstations and special server applications", explains Mag. Roland Mossig, Noctua CEO. "Due to the ever-growing demand for our Xeon and Socket F mounting kits, we decided to design new, customized versions of our coolers that are completely tailor-made for use on Intel Xeon and AMD Opteron systems, especially dual socket configurations. Enter the DX/DO series!"