Microsoft has released Windows 2008 R2 RTM for the TechNet and MSDN subscribers. Windows Server 2008 R2 is available in 64-bit (x64) only.
Microsoft is also providing Windows Server 2008 R2 180 day evaluation for the general public.
Check out the Windows 2008 R2 System Requirements at http://www.microsoft.com/windowsserver2008/en/us/system-requirements.aspx
Despite the name Windows 2008 R2 (Release 2), it is a whole new operating system. It has all new features and functionalities and not just the enhancements. For web people it has IIS 7.5.
You may also want to see this website: Convert your Windows Server 2008 R2 to a Workstation!.
PS: Windows 2008 R2 Logo - Copyright Microsoft