SugarCRM, WordPress (Automattic), Drupal (Acquia)...and a handful of others. Handful being the operative word.
There are countless others that have some commercial success. I'm Chris has had some success in supporting Swift Mailer and most authors of most CMS's probably get a contract or two.
What you need to ask is what exactly are you after?
1. Long term sustainable, full time, self employment? Odds are stacked against us.
2. Short term, subsidary income, couple hundred bucks every month or so? Much more likely.
The fact of the matter is, "open source" is equated to "free" by 99% of it's users...free as in air...not as in speech...why would anyone pay for anything they can get for free? They either need to:
a. Not be aware the product is freely available -- shady business
b. Be enticed with value added services, support, etc
If you do open source incorrectly, not only do you give it away for free, but others WILL profit from you hard work and likely NOT give back a single penny. I swear OSS licenses were written up by conniving lawyers and business men who knew/reaized developers would be dumb enough to invest thousands of hours of hard work into a single project, dump it as open source hoping to make profit, never making a single penny (with the exception being the odd donation) and said developer turns jaded.
I have certainly read far more stories about <span style='color:blue' title='I'm naughty, are you naughty?'>smurf</span> off developers (myself included) who have tried, failed, tried again, failed, etc than I have of the Matt Mullenweg's of the world (ie: WordPress founder).
My biggest grief with open source licenses, is none of them are really intended for full scale applications. They seem to protect only the source code, not the interface or data they generate. I personally think it's critical that a well designed, thoughout, planned and implemented application deserves the same rights as the source code. It takes me at least as long to plan, design, re-design an effective simple interface, so I expect that to be recognized and copyright's to stay intact.
Sorry, end of rant...just turning over in my grave here thinking about releasing a product as open source...experience tells me DON'T and reality tells me, what choice do I have and what do you have to lose???
Cheers,
Alex