I have a 40BG Maxtor drive that is virtually silent (virtually means that you can detect a low wine if you bend over and put your ear right on the thing)
My lab also has 2 80GB Maxtor drives that are quiet, but I can't vouch for exactly how quiet those are, because my lab has a lot of ambient noise
I've had experience with 2 QPS Que!Fire CD-RW drives, and they are absolutely silent. Of course, that goes for QPS's tech support, too. The way I see it, Que drives are about 10% cheaper than their competitors, but about 10% of the drives are lemons, and you're better off just eating the cost than dealing with QPS's service department. But they are certainly quiet drives.