KingSumo Giveaways is the most cost effective way to grow your audience by encouraging your visitors to share your giveaway. The more friends who enter the more entries they earn, giving you their emails. Works on Wordpress sites only.

SumoMe is an online library of free and paid apps and widgets for improving the usability, interaction and list building capabilities for any website. With just a small snippet of code embedded in blogs, eCommerce sites, product information pages and more, web developers can easily add tools such as "Buy" buttons, sharing buttons, scroll boxes, subscriber opt-ins, contact forms and many more. SumoMe is free forever with limited features, plus a cost-effective selection of price plans right-sized for any organization's needs.