Amazon offers the Western Digital My Passport Air 500GB USB 3.0 Portable External Hard Drive, model no. WDBBLW5000AAL-NESN, for $57.99 with free shipping. (B&H Photo-Video charges the same.) That's $8 under our October mention and, outside of the mention below, the lowest total price we could find now by $22. It's USB-powered and features hardware encryption.

Of note, Western Digital Store offers it bundled with a Western Digital My Passport Carrying Case for $59.99 with free shipping via coupon code "SHIPS4FREE".