mailermailer

This plugin is super easy to use. It basically makes a miniature version of the sign-up form that MailerMailer hosts for you, but puts it right in your WordPress. There aren't a ton of customization options, but it's more than enough for my purposes. Literally took me about 2 minutes to set the whole thing up. The one thing to note is that you need to sync the WordPress plugin every time you make changes to the hosted signup form on MailerMailer, otherwise your updated fields don't display.