I have had the opportunity to work with the WordPress Newsletter Plugin from Tribulant, a plugin that rivals the free MailPress plugin, but with its own twist (and its own pricetag of $54.99 single license, $274.95 unlimited).
The WordPress Newsletter Plugin copy starts out by shouting:
A WordPress newsletter plugin which will, without a doubt, blow your mind away with its feature set…
And it does, after you take a look at one of its core features that they’re proud of:
Both PHP, HTML, CSS and WordPress shortcodes can be put into themes.
See anything wrong with that?