The Buffalo DriveStation line of SATA USB 2.0 external drives gives you a 7200RPM serial ATA disk at less than a buck-a-gig. They're available in capacities from 160GB ($159) to 500GB ($449) and are compatible with both Macs and PCs.
We like the DriveStation's auto power feature that turns on and off automatically with your computer, and its fanless design that keeps things quiet when the going gets tough. Plus, you can lock up your data with Buffalo Secure Lock Ware, encrypting everything in case somebody jacks the drive from you. And, at 1.77 x 6.41 x 7.86 inches, it'll fit into tight spaces. Available now.