Making money thru open source?

The question: how does one go about harnessing the goodwill (presumably) generated by giving away your work for free?

Anybody got any good ideas? Examples of working business models, based on open-source, are especially welcome (and yes, I've heard of Red Hat.)

Anyway, I'm asking because I want to devote more time to my open source projects (i've got three), but i also need an income, and three projects + work + family doesn't seem to fit in a 24 hour day!

One thing I've tried: developing a commercial service out of a project and keeping it ahead, version-wise, of the public project. This has met with limited success. The public project is "phpMyInventory" (http://sourceforge.net/projects/phpmyinventory). The commercial service is called "Syslist" (https://www.syslist.com). I figured it had the greatest chance of success, because many, many IT guys need inventory management solutions, and there's not much quality competition in that area. Anyway, comments on my approach in this case are also welcome.

Thanks all.

-dje