If you are already publishing your newsletter or ezine, you have articles. You can write them yourself, or have them written by a freelance copywriter (see elance.com and similar sites). Distribute your articles to article directories. These are mostly free web sites that accept articles on many different topics.
Here’s a short list of highly-ranked article directories. My in-depth article on article writing is still on my web site.
How does article writing benefit you? In your article you are allowed to place links to your web site. All article directories allow so-called resource boxes, but some also allow links within the body of the article. A resource box is usually placed at the end of your article, and you can include your name, business name and any offer to entice readers to sign up to your list.