There are also appliances you can use and those have been around for a little while longer. Examples of these would be NetApp's Decru or NeoScale, which is now owned by nCipher. These are appliances that you put between your backup server or the source of your backup data and the target, which is your tape device. So, that is another form of encryption.
And of course, probably the most ancient form of encryption, is software level encryption. This encrypts your data at the server level or the backup client level and then sends it to the tape device encrypted.
Check out the entire Tape Encryption FAQ.