Windows Server 2012 is getting close now. Of course I've been playing with the release candidate. One of my favorite things so far is how easy it is to turn off the GUI, therefore turning the server into a Core installation. You can also turn off the GUI, but leave the Server Manager enabled. Another thing that I think is going to be awesome is the Hyper-V Extensible Virtual Switch. It's obvious that Microsoft listened to its customers when they complained that the Hyper-V Virtual Switch in 2008 R2 was a bit anemic/featureless. This is a huge enhancement, in my opinion, and is going to introduce some very interesting opportunities, such as migrating a VM to another datacenter without changing its IP address, etc.
There are a lot of other new enhancements. I found this free eBook entitled Introducing Windows Server 2012. Check it out; there are tons of neat and enticing bits of information in there.