I went really over the top when I started looking at how to cool the little server room under my stairs. I set up 2 120mm almost silent PC fans, running them at 9v from a variable wallwart PSU. I used an x10 to control the fans as I had a spare module and a temp sensor the server could read.

In the end they were so silent, and the x10 so unreliable, that I just leave them on 24/7 now. They have been running like that for over 4 years, I never thought cheap PC fans would last this long but they are just as quiet as when I put them in.

It seems to be a very effective solution, I have one at the bottom of the wall for intake that blows clean cool air right over the servers, and one at the top of the room kicking the warm air back into the outside room. If I turn the fans off I see the temp rise quickly, so it really works.

Cheers

Cris.