Ive got a diamondmax 250Gb sata-II 16Mb and a Samsung 200Gb 8Mb cache sata-II. The Samsung and the Seagate are supposed to be the quietest, but since getting a P180 the diamondmax accesses cannot be heard at all (rubber grommet mounting).
The only issue Ive had with either is that the diamondmax sometimes fails to be recognised in the bios (usuall after changing some setting somewhere) and requires a cold boot.
Ive used western digital (have a 120Gb not connected to pc atm), and they are good imo.