I personally prefer Western Digitals.
Sure, the warranty isnt as long, but hard drives are becoming so cheap, sometimes it might not even be worthwhile to deal with the warranty.
Besides, a general rule of thumb is that if its gonna croak, it normally does within the first few months of ownership. Thats from personal experience.
I bought 2 250GB Caviar SATA drives, and when I got them and plugged them in, I thought they were dead on arrival, but when I placed them aganist my ear, they were spinning perfectly fine. They're that quiet.
If your iMac is 2.0 GHz, its definitely SATA.
You can get a 250GB drive online for around 60-80 shipped at Newegg.