Question and Answers communities are a really great way to promote your good content. You just need to find related questions and write a helpful answer but also get them to visit your websites for more information.
I did a lot this kind of promotion over the years for many of my clients. Yahoo Answers was the best and the most popular until Yahoo decided to stop maintaining and improving the platform. At the moment it's pretty hard to still publish and promote stuff on Yahoo Answers.
The next best thing is Quora, awesome Q&A platform, lots of active users, very easy to promote stuff there.
Anyone around with experience on this subject? What other popular Q&A communities are out there?