Balsamiq Mockups

What do you use to create mockups of your UI? I prefer a very lightweight approach using a good ol' whiteboard or even sketches on paper. You can capture a whiteboard mockup with a camera, or scan a paper mock up. For distributed teams, though, you can't collaborate very well with either one of those approaches. I just discovered Balsamiq Mockups and after trying it out, it looks like a good solution. It also has a sweet integration with Confluence, Jira, and XWiki.