Are there any add-ons to Sharepoint to provide a Q&A type of site like this one or Stack Exchange? This would be for an internal corporate intranet, rather than a public site. I know there are open source Q&A platforms, but my company is strongly focused around Sharepoint.
There are some ways to do this with custom content types, possibly even building on the Discussion Boards that are out of the box in SharePoint, but if you are looking for something that might be able to be implemented quickly I would look at the SharePoint Forums from Lightning Tools. http://lightningtools.com/
I evaluated lightning tools and Bamboo discussion boards plus. I am not a big fan of Lightning tools solution, but I do like discussion boards plus:
Specifically, they build Q & A into the SharePoint discussion board functionality and have things like "Suggest as answer", "Verify as answer", etc...
You can see my review of lightning tools here: http://www.sharepointdoug.com/2011/07/quick-and-dirty-evaluation-of-lightning.html. The biggest problems at the time of my review was their disaster recovery and SharePoint integrated search stories.
I have spent a lot of time evaluating this problem and based on what you described, I think Bamboo's Discussion Board Plus is a good solution.