Popular stencils
Charts for storyboarding
A different set of charts and a table which can be used to create a storyboard or workflow for a dashboard
Apple Icons (Large)
A set of large application and system icons from Mac OS X (Part 1).
Neon Necessity
A stencil used more as a style starter for darker maps. Best used on a 50% gray to full black background.
Leopard Icons Part 4
A collection of the high-res 512x512 icons that apple uses in the finder when using the coverflow display option (Part 4).
Business Charts and Graphs
A full set of charts and graphics for data visualization in a subdued and professional color palette ideal for business. Included are bar charts, stacked bar charts, line charts, calendar views, bullet charts, pie charts, sparklines, bubble graphs, difference charts, area charts, gauges, a sankey diagram, funnel graph,...more
Feed icons
Here's a set of standard feed icons for RSS and Atom feeds. Icons come in 10x10, 12x12, 16x16, 24x24, 32x32, and 48x48 sizes, and work well on light or dark backgrounds. For more sizes and info, check out the Feed Icons website.
Basic shapes (curly brace, clouds, block arrows)
I have imported a few shapes from Visio into OmniGraffle and created a stencil of them. It contains a curly brace, a number of cloud shapes, and a number of block arrows.
iPhone 5 GUI
An iPhone 5 GUI stencil made entirely in Omnigraffle - the only bitmap image is the actual phone and keyboard. Everything is editable. Includes: Safari, Buttons, Sliders, Settings, Toggles, Camera, Notification, Map Icons, Login Form, Chat Bubbles, Photos, Multiple Icons, Copy and Pasting functions and more.
Social Media Peeps
Social Media people that you can use for charts and diagrams of communities, bloggers, Tweeps, whatever you can imagine.