Hover over "Technology Solutions". Virtualization and Management menu item.
I don't see any link to the Hyper V Server product page from there either. From there, you can go to the Try It page, and there are links to download Windows Server 2012 and System Center 2012 and also links to virtual labs. But there is no link to download the standalone Hyper V Server.
I have a feeling this product is going to be killed in favor of Azure Virtual Machines.