It looks like Microsoft are getting ready to release Windows Server 2008 RC0 to the general public soon. A search in Google for "Server 2008 Beta 3" or "Server 2008 RC0" returned the usual links to the Beta 3 download site but had a link title name of "Evaluate the Windows Server 2008 Release Candidate today". While the actual MS site lists the current version as Beta 3, Google Cache has the following updated RC0 page:
Microsoft have also already released RC0 to TAP as noted in Andy Malone's Blog.
Microsoft, Windows Longhorn Server, Windows Server 2008, RC0, Public Beta, Beta