Popular stencils
Protocol/Data Block Design
This is a 32-bit ruler and a data field for laying out protocol specification diagrams like commonly used in RFCs and similar publications.
A10 Networks
Stencil for A10 Networks Thunder Series Platforms.
Concert Stage Objects
This stencil contains backline, monitor speakers, and other symbols for musicians.
Windows 8: Dialogs
Dialogs for Windows 8.
Windows 8: Category views
Category views for Windows 8.
Human Chromosomes
A vector library of human chromosomes, copied from the public domain on Wikimedia Commons.
BlackBerry User Interface
A very basic stencil for BlackBerry. I've taken care to ensure that the representations of the devices are to scale; everything on the stencil is at 1/2 scale btw if you wanted to design in real size. Please feel free add to this stencil if you think some important controls are missing.
Cursor
This is going to seem silly, but it's simply the mouse pointer. You need it, and you need it fast.
Billard Balls
Use these in momentum lesson for physics.