There are several options available to you with HDDs and they cover brand, size and speed.
The best performing drives are listed on
www.storagereview.com
Brands: Western Digital, Maxtor, Seagate, Hitachi, Samsung....
Sizes: Up to 300GB in the 7200rpm range & up to 74GB in the 10,000rpm RAPTOR range
Speed: 7200rpm & 10,000rpm
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I have seen on Storagereview that the Hitachi won a performance award, displacing the traditional leader Western Digital. But the RAPTOR is the fastest in the SATA range.
If you have a SATA interface on your computer, you could get a RAPTOR drive, ideally in addition to a larger capacity 7200rpm drive.
I have used Seagate and Western Digital, but not the others...but I can say, that in my opinion WD is making very good drives, particularly the RAPTOR which is really fast. I have built 2 systems with raptors and they work a dream (although you learn to take it for granted fast too!)
I'd recommend Western Digital for SATA/ATA drives and Maxtor for SCSI.
Roley
Black Frog Technologies