Could be Hitachi. I think my Rev A iMac has a 160 GB Hitachi in it. I am not 100% sure, but I did have it apart a couple weeks ago and that is what I remember for some reason.
My iMac 20" Coreduo has a 250GB Western Digital, so it is a possibility that the iMac could be packin' the "Dub-D" (aka a western digital Hard drive.)
-dsm