You could do a quick Google on the subject. I came up with this site who ranked several different providers: http://email-marketing-service-revie...enreviews.com/

It depends on how many features you want the email provider to offer as well. We used Exact Target for a while, but in all honesty, we never used half the features and their stystem had technical difficulties far too often for me to recommned them. We've also used Constant Contact who are good, but if I'm correct their services are pretty basic.

Hope you find a good fit.

Martink