I use Herculist every day without fail and I love it!
It's a large, well-established mailer with almost 90,000 members.
The Gold Membership is only about $25 for a full year and that allows you to mail the entire membership every single day!
My upgrade paid for itself several times over within a few short days.
Admin are great - commission withdrawals are processed within 24 hours (often a lot less) and there's loads of different advertising options, including a built-in traffic exchange.
Thoroughly recommend it.