My Email Marketer has a "send to friend" function that is easy to set up.

See below for a quick overview of the process.

1. You create a “send to friend” form and customise it.
2. The user clicks on a “send to friend” button or link in the email campaign.
3. User fills out the “send to friend” form.
4. Friend receives the same email with a header saying it has been forwarded from their friend’s name (the subscriber) and their friend’s email address.