My add-on Postmaster is already available and by far the most comprehensive email solution for ExpressionEngine. It has a series of robust API's developers can extend to do really custom stuff. But'tBut it also includes UI's and plethora of options to send emails at just about any time without writing any code. v1.3 is in beta and brings a whole new Notifications API in the mix for cron notifications, among other things. I have over a year of development in this add-on and it's only going to continue to improve.
Postmaster even supports a huge variety of services like Mandrill, MailChimp, CampaignMonitor, SendGrid, MailGun, and more. I am adding new services all the time as people need them.