The server got a major upgrade this weekend. I had to replace the power supply that died so I bought a more reliable one, the Antec TruePower Trio 550. Look at the size of the fan! 120mm and very quiet.
At the same time, I upgraded the CPU from an Intel Pentium D 820 to a Core 2 Quad Q6600. Nice!
Of course, I also had to upgrade the CPU fan 
I bought an ultra silent ASUS Silent Square.
Left is the ASUS fan, right is the stock Intel fan.
With all that cooling, the server is surprisingly quiet because of the quality of the parts but also because of the size of the fans.
