I'd recommend a Hitachi Deskstar 7K1000 with 32MB cache. I have upgraded my white iMac 24" with this drive and I am very pleased with its performance, heat output and generated noise.
how can you have a white imac with a 1TB hardrive? i thought only the Al imacs were openable, how can you open a white imac? the screen is behind the white structure, the Al imac, its right on level, and removable with suction cups