Two magazines that regularly help me learn more about managing Windows server systems are WindowsITPro and Microsoft’s own TechNet magazine.
One reason that I love WindowsITPro is the searchable online archive. It’s worth subscribing just to get access to all of those articles.
Microsoft’s TechNet magazine is available online for free, and also contains a lot of good information. I especially enjoy the Scripting Guys. They have a column in the magazine, and you can also just go to the Microsoft TechNet Script Center.