You can build your list simply by writing articles, whether you have thought of it or not.
Quite simply, you write and submit your articles on your topic of expertise or business nature to popular article directories where eZine publishers and readers are looking for the information you provide.
Leveraging your viral marketing efforts on article writing can be rewarding, if done right. In the real sense, you are actually proving your worth and demonstrating your expertise about your business through the articles you write.