I have been updating some of my Visio diagrams lately and wanted to use stencils that were more realistic and stumbled upon these Dell provided stencils. Just follow the link below.
http://www.dell.com/content/topics/topic.aspx/global/products/pvaul/topics/en/visio?c=us&cs=555&l=en&s=gen
Enjoy.
–Himuraken