For over a year now, I've been running Sparrow Mail for Mac, and it's been a great, streamlined solution for email. A few weeks ago, I installed the new Sparrow iPhone app, and I can tell you— it's fantastic. Great design solutions are about solving problems, and quite-frankly they've killed several Apple dragons that have been circling around the default mail app for years.
To best demonstrate several of the key interactions available on the app, the folks at Sparrow have added several animated click-throughs to the iPhone app's website. This simple solution allows the visitor to quickly become a "user" of the iPhone app, and better than that— this click-through probably converts many a customer.
I recorded a quick video and posted it below.