I use Visio for creating plans and diagrams for SharePoint sites and farms frequently. When doing so, I like to use the actual SharePoint graphics as stencils. I have compiled the graphics from SharePoint 2010 as well as some file type icons into Visio stencils. I make heavy use of these and have attached them so that others can take advantage of these as well.
Please note: The stencils may not have all SharePoint icons and graphics, but they have the majority of them. Also, some stencil graphics have been named while others have not been.