For your edification and amusement, a site that enables you to Barcode Yourself.
At least, using a standard US-pattern 12-digit Universal Product Code barcode ( UPC-A). The rest of the world uses a 13-digit version, the European Article Numbering (EAN) code. There are 8-digit versions of both too, and the EAN often has a 5-digit extension, just to complicate matters. With the extension, the barcode can express an ISBN (International Standard Book Number) or equivalent for other articles.
The US and Canada will be gradually switching over to EAN over the next few years, so alert readers in North America might want to check to see how the changeover's going : 12 digits = old, 13 = new.
The Barcode Art site has other interesting things in it apart from the "Barcode Yourself" bit. There's a particularly neat Barcode Clock that's freely downloadable. But by far the most fascinating part of the site is the gallery of barcode portraits. It was a Revelation.