OmniGraffle is fantastic. Its useful, shiny, and it allows me to show people what my thoughts look like visually, even if it scares them a bit. Perhaps one of the most useful applications of OmniGraffle is for plotting out infrastructure of some kind; network maps; flow charts; company hierarchies. The only issue with OmniGraffle out of the box is that it comes with a fairly paltry selection of symbols and shapes to use when creating your masterpiece. Is that purple square the Executive VP of Finance, or is it the refrigerator in the break room?
Lucky for those of us too lazy to go looking for images on our own, Patrick Crowley of iCalShare has setup Graffletopia, as site dedicated to OmniGraffle stencils. (A stencil is a collection of reusable images or symbols.) Some of the stencils available are amazingly well done, and include such specific categories as Cisco network switches and Sun server hardware.
All stencils are provided free of charge, and users are encouraged to submit their own.