I'm one of the co-founders at Binpress (http://www.binpress.com), which is marketplace for commercial open-source projects. Unlike Codecanyon, which someone else mentioned in this thread, our focus is on professional development and components that are more than simple scripts. Cocoacontrols (https://www.cocoacontrols.com/) is another good example, with some of their commercial components doing very well.

We have several developers making SV comparable salaries from publishing on our platform (in the 100k$ range annually). I believe this can be a huge market - if you look at companies selling licenses to code or SDK binaries, there's quite a few who built very profitable businesses around it.

Very well known examples of companies selling code licenses include MySQL and Magento (through their enterprise versions), though they provide complete solutions and not components. Gravity Forms (http://www.gravityforms.com/) a wordpress plug-in, is another good example - it generated millions in revenue if you trust their installation counter.