I have been using two of the following: Bay Cooler II No fancy LCD or temp readouts, but very reliable (especially the fans).
One I got in 1998, the other the end of 1999. Both have run almost continuously. They carry a 5 year warranty.
These will kept my 160G WD SE drive barely warm to the touch, even after extended use. Without them, the drive seems like it would get hot enough to cook an egg. (No I did not try to cook an egg on it).