The Seagate Maxtor BlackArmor is a marvel of simplicity. It's the first external hard drive with full-disk encryption - the encryption chip resides on the hard drive's circuitry.
According to Seagate, all of the data is encrypted on the Maxtor BlackArmor drive, so even if someone removes the drive from the housing and takes away the chipset, the data is inaccessible.
When you first attach the Maxtor BlackArmor to a Windows PC, the drive loads a read-only partition with the setup software. Initialising the drive and setting a password takes only a minute, after which the drive loads the encrypted partition and Windows shows it as a drive letter.
Thereafter, every time you plug in the Maxtor BlackArmor drive, the autorun settings will ask you to enter the password.
The Maxtor BlackArmor also features a Secure Erase option (which overwrites data areas of the drive with zeroes), as well as a backup utility.
If you're looking at encrypted portable drives, this model is up there with the best for its value. The Maxtor BlackArmor offers one of the best cost-per-gigabyte rates we've seen, as well as first class simplicity and full-disk-encryption security.