I bought a 73gb 15000 rpm hard drive for only $40 including shipping on ebay. The drive is the Fujitsu MAU3073, the smaller brother of the equally amazing
Fujitsu MAU3147. The MAU3073 is exactly the same as the MAU3147 except for less hard drive platters so performance will be identical. It's a Ultra320 SCSI drive so it will require a SCSI controller but even with the additional ~$30 for the used controller it'll be well worth the price.
Despite being nearly 4 years old these drives still slaughter newer, high capacity SATA drives primarily because of the 15,000rpm speed vs 7,200rpm and the Ultra320 SCSI interface. Here's the transfer graph of several other SCSI drives compared to the Fujitsu MAU3147 and the Raptor WD1500ADFD (highlighted), one of the first 10,000rpm SATA drives:
As you can see the Fujitsu MAU3xxx easily dominates all the 10,000rpm drives and beats all but one 15,000rpm drive.
But transfer rate isn't really where the Fujitsu shines, it's the access time that's truly impressive:
5.5 ms! That's over twice as fast as the ~1 year old
Hitachi Deskstar 7K1000, a 1 terabyte 7200rpm drive that was one of the first to
incorporate perpendicular magnetic recording.
Access time is important because it's the amount of time it takes the hard drive to access a particular file. Think of it like a CD player and you're trying to skip from track 1 to track 15. Imagine one CD player takes 13 seconds to skip to the next track and the other player takes 5.5 seconds. Which would you prefer? So think of the Hitachi Deskstar as the 13 second CD player and the Fujitsu as the 5.5 second player.
So as you can see even though this drive is 4 years old modern SATA drives don't even touch it's access time or transfer rates. Well worth the $40 + cost of the controller.