Commissions: $5 per free signup. $105 for each paying customer.
Constant Contact is one of the most famous email marketing services on the web.
In fact, I use it myself for the Affiliate Marketing Pro newsletter.
It allows website owners to build email lists that they can send newsletters and marketing to. This can be a hugely profitable way to do online marketing. It has been referred to as a way to build a legal money printing press in one marketing book. I believe it was in the book Launch, by Jeff Walker.
To my delight, they offer a very high paying affiliate program with commission rates of $5 for free trial signups and $105 for paying customers.
That is great considering a subscription does only start at $20/mo.