Might be of use to someone..

ISBN barcodes use EAN13. This hacky evil thing will take an ISBN on the command line and produce an EAN13 barcode, along with the required human-readable bits (the original ISBN and the generated EAN13 code, which has to use a different formula for the checksum and needs '978' tacked on the front). It'll spew the result to STDOUT. perl codeEAN13.pl isbn | pnmtopng > out.png works nicely. Whitaker link to a load of places that appear to charge for the privilege, for some reason.

Update: Now in handy online form.