According to this review in Tom's Hardware...
...the latest Hitachi drives have the fastest random access read times this side of a Raptor.
I don't own one, so I can't say how quiet or reliable they are, but this might be the best solution for a 7,200 RPM sample drive.
Sure, you can get a Raptor, but they're less than 1/3 the size, and are likely louder, due to their 10k speed. Dollar per GB is likely better with the 7,200 rpm drives as well.