This program works as expected, and offers a good deal of formatting options for various types of barcodes. Don't forget to download the free registration key at pro-barcode.com to get rid of the 'EVAL' letters.
There are free OCR-A and OCR-B fonts on the web, so you can make the barcodes really standards-compliant.

However, when decoding the datamatrix codes that this program produces, I often get incorrect results with longer strings. I'm not sure if this is due to errors in the decoder I'm using, or the encoder in this program. So you should verify this if you intend to use this program to generate datamatrix 2D-codes.