Microsoft Office Professional Plus 2013 is now available for download to TechNet and MSDN subscribers. SharePoint Server 2013, Exchange Server 2013, Lync Server 2013 are also available.
The Office Professional Plus 2013 DVD image (ISO) can be downloaded from this page. The ISO is available in separate x64 and x86 versions.
All those who buy Microsoft Office 2010 on or after October 19 will get a free copy of Office 2013 when it ships in the first quarter of 2013.