Announce-list advice (app or 3rd party app/service)

I’m looking for a free or reasonably-priced app or 3rd party mailing list service, like mailchimp, that offers features like:

wordpress integration
subscribers/leaders (who cannot post)
contributors (who can post but with moderation)

Additionally, all subscribers are recipients of all emails, but "Leaders can be flagged as recipients of only leader emails.

Mailchimp, as far as I can tell, doesn’t have the ability to have a subset of subscribers.

Anyone have experience with any of the services out there?

– Phil

I don’t have a lot of experience on this myself either, sorry. The only thing I can imagine for this is some wordpress plugin that lets you send posts via email. Since WP has the concepts of users and roles, maybe you can hack something together that way. Let us know if you find anything.