Of all the email newsletters I receive, these are the ten best designed. All are excellent in a different way, so there's no ranking.

le cool – most innovative

Publishing Perspectives – best example of curating a topic

ClickZ Experts Today – most effective at humanizing news and opinions

Promo Xtra – best at discovering valuable tidbits

First to Know – best at showing what news means (relevancy)

Fast Company – the glitziest take on technology and business trends

Springwise – best use of imagery to convey ideas quickly

Fetchdog – most beautiful overall design

Flavorpill – best information architecture

Michael Katz's E-Newsletter on E-Newsletters – best writing