I read two really good direct marketing magazines: Direct and Target Marketing. The magazines’ coverage includes e-mail marketing and many other marketing related issues. What really makes them good is that they are so well written, as, I suppose, you might expect from a group of people who make a living writing copy.
Denny Hatch (in Target Marketing) and Hershell Gordon Lewis (in Direct) always write very entertaining columns that always pack a thought provoking punch. There are always several other articles that are worthy of clipping.
So, whatever sort of marketing you are in, I highly recommend subscribing to these distinguished publications.