The AWeber website is super popular according to their Alexa traffic rank and their sheer number of customers, which is currently over 100,000.
You can earn a neat 30% recurring revenue share when promoting AWeber. Currently, they charge $19/mo for the plan that allows for up to 500 email list contacts and substantially more for the larger plans.
Entice signups with a 30-day free trial.
Their email marketing features include email newsletters (naturally), drag and drop editor with over 700 responsive email templates, email automation, split testing, and much more.
I like that they have made it possible to make affiliate tracking links pointing to useful content like their blog, webinars, and videos.
I believe you can also make links to any page of their website by just applying your tracking parameter at the end of the link, but I would confirm that with them before doing so.