After reading a post about making your own Albert Heyn bonus cards, I search a bit around, and quickly discovered barcode (duh), a Unix command line program, which makes barcodes of an excellent quality (in PostScript).

Most barcodes on items here in Europe, are in EAN-13 code, which you find explained here. The first 2 or 3 characters are used for country codes. For example, Belgian manufactured goods are labelled with a barcode beginning with 54.