Newegg has SAMSUNG S2 640GB USB 2.0 External Hard Drive HX-MU064DA/G22 for $113.99 + free shipping.
Model
Brand SAMSUNG
Series S2
Model HX-MU064DA/G22
Performance
Interface USB 2.0
Capacity 640GB
Physical Spec
Form Factor 2.5"
Dimensions 4.37" x 3.22" x 0.69"
Weight 0.38 lbs.
Features
Features Two ways of backup : Scheduled or in real-time
SecretZone : Secure area for my private contents
SafetyKey for protecting your precious contents
Easy to set up, easy to use
Capacity Gauge through tray icon (Windows O/S)
Manufacturer Warranty
Parts 3 years limited
Labor 3 years limited
SAMSUNG S2 640GB USB 2.0 External Hard Drive HX-MU064DA/G22 $113.99 FS 
