Quick Update from Microsoft about System Center 2012 R2 Preview is available for Download from MSDN /Evaluation(below).
This prerelease version is not supported in a production environment and is for testing only.
This prerelease version does not support an upgrade from previous versions of System Center 2012 Configuration Manager. Install this prerelease version as a new installation of Configuration Manager. In addition, Configuration Manager does not support the import of objects between different versions of Configuration Manager.
To know more about Release notes and Known Issues with SCCM 2012 R2 Preview Release http://technet.microsoft.com/library/dn236347.aspx
I have just extracted all the direct download links for the System Center 2012 R2 components that will save time without Sign in Required.
Content is in Size 680 MB after Unzip.
Download the Evolution products directly using below links.
Download Configmgr / SCCM 2012 R2 from here
Other System Center 2012 R2 Components are
Download SCOM 2012 R2 from here
Download SCVMM 2012 R2 from here
Download SCSM 2012 R2 from Here
Download SCO 2012 R2 from here
Download SCDPM 2012 R2 from Here
Download SCAC 2012 R2 from Here
Download Windows server 2012 R2 from Here
Update: David oBrien blogged about New Features about SCCM 2012 R2 (whats new in SCCM 2012 R2) http://www.david-obrien.net/2013/06/25/configmgr-2012-r2-whats-new/
For more information check http://www.microsoft.com/en-us/server-cloud/system-center/system-center-2012-r2-configuration-manager.aspx
To know more about what's new in SCCM 2012 R2,read Henks blog http://henkhoogendoorn.blogspot.de/2013/06/updates-and-new-features-in-configmgr.html