There are a few community promoted ads that have commercial purchase options.
The question open for discussion - should we allow ads to be posted for products that have free versions but are still commercial?
I don't have any problem with commercial software being promoted.
For example Camtasia is simply the most user friendly software for making screencasts and for example Snagit (also from Techsmith) is a great tool for making screenshots.
While Open Office is a great initiative, I found myself a lot less productive without Microsoft Office.
However, when browsing through our very own Must have Windows programs- question, these were the only two I could come up with from the highest voted results. So what's my point? There's not that much great software out there, that doesn't have a better free alternative!
Furthermore, because there's being voted on the ads, users will decide whether or not they want to promote a product. This also means its futile to make a (spammy) ad for your own product, because the users will vote it down with a vengeance.
So I'd say: let the community take care of it, unless something very bad happens.