The one weekly newsletter which I subscribe to and read religiously is Windows Secrets. This site gives an unbiased and tremendous perspective on Windows and how to make Windows work better for you. I subscribe to this newsletter.
There is a free version to the weekly newsletter and a paid version. This newsletter provides essential tips and techniques for Windows XP, Vista, IE, Firefox, Microsoft Windows Update and much more. If there is one weekly newsletter that I recommend hands down is Windows Secrets.