The WD wd6400aaks would have to be one of the fastest. Has high density platters.
These are very fast drives I have bought 2 to make an intel matrix raid setup. Short stroked them for a 80gb raid 0 and the rest another raid 0 volume.
Again these are very fast, I downloaded the hitatchi f-tune dos hardrive tuner to set the aam to 254 instead of the default slow-n-quite standard setting.
These drives new high density platter versions with the two 320gb platters.
My 80gb raid 0 volume on 2 of these drives has a Random access of 7.6ms, an average read of 223.8MB/s and a burst speed of 3159MB/s.
The remaining space on the drives is a raid 0 1.1TB array which has a respectable 13.2ms response time (random access time), 179.2MB/s average read and a 3145.5MB/s burst speed.
These scores are form a HD tach long test.
I used 128kb stripe btw.
Truely great drives.