From a security perspective I like

"Protect Your Windows Network" by Jesper Johansson and Steve Riley - Microsoft's "original" security gurus

The Microsoft security and threats and countermeasures guides are also good resources, which one is right for you depends on which version of Windows you are using, just use "Microsoft <WINDOWS VERSION> Security Guide" in google, i.e. "Microsoft Server 2003 Security Guide"

From a general admin perspective I am not really sure but I have usually found the various (and there is a lot) Microsoft guides pretty good