Amanda supports barcode labels with the changer script
`chg-zd-mtx' (v. 2.4.4-p1).
Note that you still need to `amlabel' the tapes;
amanda maintains a list of barcode-labels vs. amanda-labels
in a file called `changer-barcodes'.

You can probably print your own barcode labels with GNU barcode.
Here's how:

Dell PV132-T in `enhanced' mode, up to 16 characters:
barcode -o code.ps -e code39 -umm -g75x15 -t2x15 -p160x297 -c
(barcode 0.98 on Debian woody, A4 paper)