As an exercise with PHP and the gd library, I wrote a couple of scripts a while ago that would generate UPC-A and UPC-E barcode images on the fly. I've always been fascinated with barcodes and scanners that read them.
Nice, most complicated part for me was getting images "up to the spec.", since I am mostly competing with desktop software, that pre-install drivers and fonts my EPS files needed to embed OCR fonts (it took tons of time to produce them accurately).
Here is the proud result (rasterized back from PostScript):
http://jazzychad.com/barcode/