What's a good tool to automate Windows server configuration, a la Chef on *NIX?
I know that Chef is somewhat working on Windows, but I'm sure there are some more full-featured tools that others are already using.
(This is an old question, but) You can use Chef on Windows now, and it's support has been continually improving.
If you have money to burn you can buy MS System Center Configuration Manager
Otherwise you can put something pretty close together using group policies and custom scripts.
You can also (since June 2013) use the Windows Desired State Configuration PowerShell tools
This video is actually quite a useful introduction to the new toolset: http://channel9.msdn.com/Events/TechEd/NorthAmerica/2013/MDC-B302#fbid=InraqmsI9ZP
However, unless you are absolutely certain that you'll never need to provision a single Linux box, I recommend you use Chef.