There are several:
Sendy - Self hosted. You would need Amazon SES as an SMTP provider at the back-end. Very low cost option.
Aweber, Mailchimp - SAAS. Pure newsletters. Go with Aweber if you are into aff marketing. In general, Mailchimp scoff at aff marketers.
Infusionsoft, Ontraport - They provide newsletter services and much more. If you want to integrate marketing automation , these are the services you should go for.