Amazon.com is a good case study of smart permission email marketing.
The emails are personalized with my name.
They send recommendations based upon what I have bought in the past.
They send recommendations based upon what people who share my interests have bought.
All of this data is uniquely targeted to me; no other person has the same set of interests and has bought the same combinations of books and music on Amazon that I have. Yet, the email content remains relevant to me. Otherwise, I would have unsubscribed long ago.
They also make it easy to order, and much of the functionality described above is duplicated on the website, if you log in.
They allow me to create my own sense of community on their website (wish list, writing reviews) and use email to keep me connected to that community.