It seems like NetworkWorld has a feature like this every single week: "Nine Open Source Companies to Watch." Well, once a year, anyway. :-) It did one last August, too. (Datamation also did one on open-source projects to watch, which I find more interesting because project-based articles are less susceptible to being gamed by PR firms than company-based articles.)
Many of the companies in its list are somewhat unremarkable, and one should be listed under "Ones You Should have Watched," because XenSource is being devoured by Citrix. But I quibble.
Last year's list was much stronger (despite there being many more interesting open-source companies this year than last), but I was glad to see MuleSource get a mention (open-source Enterprise Application Integration), as I continue to think it's one of the few truly interesting open-source companies. (Yes, I'm an advisor to MuleSource. And yes, I'm an advisor because I think it's one of the few truly interesting open-source companies.)