My buddy Kevin Greene just released Visio stencils for SCVMM 2012 R2 that he created. You can find them here.
Here you can find a download link to the new Data Warehouse Architecture Diagram. Thanks Travis for sharing.
Here are some free SCCM 2007 Visio Stencils published by Jawad Qazi on the Technet Gallery.
Microsoft release for download new Visio Stencil. The stencil contains more than 300 modern icons like Windows Server, Skype, Skydrive, Azure Cloud, Android, iPhone, Doman Controller and many more. You can download the package from here.
Larry Rayl from Catapult Systems updated the Visio Stencils so they can reflect to SCOM 2012 (RMSe, Resource Pool and etc.). Download link and more about the Stencils you can find here. Happy schema creating .