SCSI isn't worth the price for the average user, only really worth it in servers.
SCSI stands for Small Computer System Interface.
You need a PCI controller card first of all. This basically just lets you plug in SCSI devices. It costs anywhere from $50 to over $1,000. Then, you'd need an SCSI drive. Quickly browsing newegg, they cost $150 for a 36 gig 15,000 RPM drive.
You could RAID 2 74 gig Raptors for that price.
C2D E6600 | 4GB DDR2-800 | 9800GTX+ | Asus P5B-E | 150GB Raptor | 320GB 7200.10 | 750W Xigmatek PSU