You could run a giveaway with a product related to yours. Giveaways can be a highly cost-effective way of growing an email list. Curating a selection of related products that your users might be into allows you to target market segments much more precisely, as your email list will fill up with people signing up to try to receive a product similar to yours. SumoMe provides a step-by-step of how to organize your promotional giveaway, as well as a great tool to put your giveaway into action.