I use and love ListMailPro,
which I use on all of my websites. When I bought it, it was
$100, which is more than reasonable (actually, I think it's
still only $100). It offers unlimited subscribers, unlimited
lists, and unlimited messages. You install and run it off your
own server. And you can even schedule your broadcast messages
so you won't forget to send them out (like a newsletter
issue -- it's what I used for every issue of the old
Netrepreneur's Notebook).
You can add custom codes, personalize each message, add
custom HTML signup pages; you can back up your lists; and
there's lots of follow-up messages available (I've never
used them all, so I don't actually know how many there can
be). There's lots more features, too... but you can see it
for yourself by viewing
their demo.
Of course, nothing's perfect. Ideally I'd like to see the
ability to blacklist as well ... and it would be nice to
partition each list into 'sub-lists'. Of course, I have
an old version; maybe these are available in the newer
version, but I don't know for sure.
Still, you just can't beat it for the price. It's not just
the price though -- it's been a couple of years now since
I started using it and I still love it for its ease-of-use
and dependability. No doubt there are many more 'feature-
rich' autoresponders out there... but this one is great if
you need something functional, flexible, reliable, and at
an affordable price. Check it out here.