I don’t really get to crazy about software or tools, but these two are excellent.
Balsamiq http://www.balsamiq.com/products/mockups is the best thing for quickly getting you ideas down on paper and documented. I have been trying to convey concepts for an iPhone application I am writing for quite sometime with no success. I resorted to just writing the code to see the app…. waste of time!! I am on my third revision of the application.
This time around I am using Balsamiq to mock up the UI, put together a presentation, document explaining the approach, and getting document feedback.
Still a little rough around the edges, but it can get the job done for cross platform application development. i will be writing more about phoneGap in the future since I have started extending my application with PhoneGap Plugins and I need to get back to the Android version of the iPhone application I am writing.