http://www.microsoft.com/en-us/server-cloud/windows-server/v8-default.aspx
Available as a .vhd or .iso
.vhd is a great option as I currently have a Server 2008 R2 machine with Hyper-v role installed, makes life easy.
Anyone else giving it a try? Think I will also grab the .iso so I can play with the new Hyper-v features as well.