I read about Balsamiq Mockups today over at the Atlassian Developer Blog. Balsamiq Mockups looks like a nice tool especially since it integrates into Confluence. It looks like JIRA support is coming too. Maybe I’ll get a chance to look into this more later.
For today, I opted to use OmniGraffle. Fortunately I found the Yahoo Design Stencil Kit which made the job even easier. They have stencil kits for Visio and Illustrator too.