At the moment I'm using these (Vantec Vortex) in some of my machines:
They seem to be pretty good but because of the strange fan, they make a bit of a mechanical whirr (Hard to describe). I'm buying some new equipment soon, so I thought I'd try something different. I may try and silence the machines a bit and go fanless, but I'm not sure. These are the different coolers I'm looking at:
Vantec HDC-502A (Probably noisy)
Coolermaster Cooldrive 6 (Looks good, quite quiet, very expensive)
Zalman 2HC2 (Silent, expensive for what it is, not sure how effective it would be)
AeroCool HB101 (Same as Zalman)
SilverStone FP53 (Fairly quiet, reasonable price)
Does anyone have any particular opinion on any of these? Are there any others that people have used and think are good buys?