Inspired by this question:
What tools are available to audit security on an existing Windows server, say Windows 2003, for my case, but what else, for which Windows Server version?
What can I do to test the existing protections on the network?
I'm looking for tools that can identify configuration errors, common and less common flaws, known issues, antivirus tools, any tool at all that can help identify and fix problems in the server. Extra bonus karma feel-good coffee bean points for tools that can be used network- or domain-wide.