People think visually. A picture is worth a thousand words as the saying goes.
We’ve recently been using Balsamiq to put together wireframes we use to work out user experience concepts, and to work with stakeholders. Balsamiq is an Adobe AIR-based desktop application that can be used to quickly put together web and mobile UI wireframes. It’s also relatively easy to make clickable demos in Balsamiq by stringing together screen wireframes.
What I probably like most about Balsamiq, is the wireframes have a rough and unfinished look to them. They get the point across, but purposefully look informal so people focus on the general concepts and information presented on the UI, and not the color or exact positioning of buttons.
If you’re an OmniGraffle user, there’s some stencils that are also a good option, among them Konigi, and Yahoo Design Stencils (also available for Visio and in other formats).