I'm in the research phase of my work report "An Analysis of Source Code Documentation Tools" and am looking to poll the waters, primarily the waters populated with those who work in proper companies.

My knowledge of the commercial lineup of source code documentation is directly proportional to the number of Google searches I do on the topic and sadly, this isn't going to cut it for me. My poll to you therefor is a rather open-ended one.

Which source code documentation software do you use in your workplace?
If you are using a commercial product, why did you choose such a product over an open-source equivalent?