Discussion boards are one of the great places to tap into your target audience. They are where people hang out. Approaching such a forum strategically, you can drive traffic back to your blog quite easily.
Do Not promote your site directly. Just contribute and build your name first. After you establish your expert status there, whatever you put in the signature in the forum, people will visit because they know you provide solid advices and content related to the topic of the forum.
Other experts often also hang out in the same forums. This can lead to joint venture and other opportunities that you may not realize right now. If they own a blog, you can also cross promote each other.