OCAU has a new HDD cooler that they just finished testing. Go see their take on the Macase MS-10 "Hermannator" HDD Cooler. here's a snip:

"At the front, behind a removable dust filter there are two 40mm Sunon ball-bearing fans. These are very thick, much more so than the 486-cooler type 40mm fans more commonly seen. Being Sunon they give you some reassurance of reliability and as there's two, should one fail your drive will still be cooled. However, there is no facility provided to monitor the RPM's of the fans so you won't know if a fan fails unless you are actively monitoring the HDD temperature or removing the dust filter while the unit is powered. The air is directed both along the top edge of the heatsink (among the fins) and straight into the back of the drive. This means that some air flows under the drive as well, helping to cool the electronics. Realistically though, most of the heat from a HDD is generated within the HDA area so that's where the focus should be - and is, with this design."