Popular stencils
Bantik UML
Because UML doesn't have to be black and white... Version 2 turns the 'object' object into a table, making adding an attribute, method, or private method as simple as command-enter.
Isometric Icecubes
Colourful, scalable isometric blocks useful for making layer diagrams or pseudo-3d illustrations.
Apple Server and Storage 02-08
Apple Server and Storage, for diagraming Apple Enterprise environments
Cubicles
You can make your own office layout with these desk and cubicle shapes.
Web Detail Flowchart
The page title, page file name and page description area labels are editable. I added an example of how I use this stencil. Feel free to use as you like though.
Formal Network Symbols
This is an excellent stencil set of formal network symbols, for when the poofy internet cloud simply isn't enough. Oh wait — the poofy internet cloud is still there, hiding behind the moniker of "Network Cloud". That seems formal, maybe not black tie, but pretty formal.
Monotone Servers
Simple monotone servers
UX Arrows
Arrow set for use on your charts, diagrams, and illustrations of information, ideas, and concepts. Use in conjunction with UX People, US Human Figures, and UX People Builder stencils. Optimal for information architecture, interaction design, and user experience projects.
Dialogue Balloons
Comic-book bubbles!