It's not clear who owns the Hillary4McCain.com site:
On the web, someone prepared in advance for the anticipated wave of Clinton supporters by registering Hillary4McCain.com on May 31st. Clinton gave her concession speech June 7.
As you can see, there's a bold landing page picturing the two senators together. It then re-directs visitors to McCain's site.
The only problem is that the domain name registration information appears to be false.