I know mailchimp has a great built in design solution and campaign monitor also one that is very cool. Do you recommend any others?
Zurb just released Ink which seems really nice: http://zurb.com/ink/
Zurb Ink looks cool, I've been using this responsive template of theirs: http://zurb.com/playground/responsive-email-templates
and Putsmail is an excellent free to for inlining, testing: http://putsmail.com/
Putsmail inlines CSS only in the preview though not when sending the actual mail anymore.
Yesmail. http://www.yesmail.com (yes, I'm a little biased) Ultimately email equates to late 90's html, so testing is critical especially with responsive design. Fresh creative and engaging content wins the day.
I've seen and used several different email marketing services.
My company uses Constant Contact, which isn't the worst in the world, but it's far from what MailChimp and Campaign Monitor offer: those two really are the best in it's class.
http://litmus.com/learning has some really great articles and best-practice posts as well.