Well, we use Groupmail in the office. It
is free if you only send out 100 emails at a time, but if you want more, you have to pay (around $99 if I can recall).
It is horrendously usable, and it does make sending out e-mails a breeze, the only issue, like most emails sending programs, is that if you are using your server, your server could easily grind to a halt during use.
However, it's the same with all programs, but Groupmail allows you to send it over your outlook connection, or even sending it directly (which nobody will shout at, though unfortunately less e-mails get through).
Other than that, I know a few people use Pommo on these boards too, so you may be interested in that.
Links:
http://www.group-mail.com/
Main Page - . .. poMMo .. .