http://freebarcodefonts.dobsonsw.com/index.html
http://www.idautomation.com/fonts/free/

There are many more, just do a quick Google search to see.

While there is merit to using image-based barcodes (consistency, ease of deployment, etc.), I prefer to use fonts because they tend to be easier to work with in FileMaker, and they are more versatile.

http://posworld.com/onbargen.html

has a wider variety of generators than barcodemill. They seem much peppier and their terms of use seem vague to benevolent: “Create barcodes online for testing or whatever you like! No need to give us your email address or worry about us charging for this service in the future. ”

With a little poking around the source, it’s easy to see how to formulate an image URL to use in a web viewer.