In an effort to remain current in the email marketing world, I am subscribed to about a dozen or so mail lists of senders who, in my opinion, push the limits of email marketing design.
I would like to know which senders you follow.

To kick it off, here are some off of my list:
Email on Acid
HBO
Litmus
Lumosity
Redbox
Seagate
Smashing Magazine
T-Mobile
UGG
Zurb