At my company, our product owners like to sketch things out in basalmiq, layout-mockup software that makes it easy to give a rough outline of what the various product screens should look like. What's nice about basalmiq is that everything has a clean but crude look, as if someone with a very clean style was sketching it on a whiteboard:
The deliberate crudeness lets people reviewing see the bigger picture, and not got tripped up on commenting on small details of the design. (As is the reviewer's wont, I know from personal experience.)
The program's "presentation mode" has a beautiful UX detail I simply adore. It features an oversized mouse pointer, so that people in the back of the room can see what you're pointing to. But MORE than that, they have the pointer rotate so that it's always directed at the center. It took me a second to realize that was the simple algorithm they were using, because in practice it does a terrific job of subtly grabbing the eye and really seeing what's being pointed at.
I used processing.js to mockup a replica of it in action, full of this that and the other... (my apologies, and sympathies, to users of older versions of IE)