You can Google this topic. I did and came up with this site: http://email-marketing-service-revie...enreviews.com/ They list Constant Contact as #8, who I've used - good company, services are fairly basic. I don't recommend using Exact Target; they offer a lot of complex services which you may find useful, but we ran into serious technical difficulties for which they couldn't provide adequate or timely support.

I suggest first making sure you know what you want and how you want to implement features. Then research the companies out there to see who is a good match given your budget. Don't sign a contract for services you're not sure how you'll use even if they are cool, because you might not implement them and then you're paying more than you need to each month.

Hope you find a good fit,
MartinK