You can now download the Windows Server 2012 R2 Preview from the TechNet Evaluation Center. I am installing Windows Server 2012 R2 Preview into a virtual machine on my home server as well as an Azure VM as I write this post.
The download is conveniently available as a .ISO image, as a mountable .VHD file (for both Datacenter and Core installs), as well as a Windows Azure VM. If you don’t already have a Windows Azure Trial account, this is the simplest and fast way to test out Windows Server 2012 R2 Preview. Just sign up for a Free One Month Trial of Windows Azure, then provision a new Windows Server 2012 R2 Preview VM!