SketchyPad (US$4.99) is an iPad app using a simple sketchpad metaphor and a lot of stencils to make mockups. It includes many of the design elements that are used in web design and app development. The app includes snap-to bluelines for aligning elements, the stencils can be locked in place with a lock icon, and there are tools for layering buttons and other elements on the page. When you're done with a sketch, it can be exported to your camera roll, emailed, or exported to Balsamiq Mockups for Desktop.
There are a few things that are missing from this early version; it would be nice to be able to rotate elements like the iPhone and iPad mockups on the screen to show landscape orientation, and display mockups through the VGA adapter for collaborative design sessions.
Compared to iMockups ($9.99), SketchyPad does not include the fine controls for arranging or sizing elements. On the other hand, SketchyPad is less costly and, at least for me, has a much more intuitive set of controls. The most powerful feature is the exportability to Balsamiq (not included), which means that SketchyPad drawings can be linked for quick and easy rapid prototyping.
It's wonderful to see that app and website designers have a choice in terms of wireframing tools on the iPad, and I look forward to seeing how both SketchyPad and iMockups evolve. Several screenshots of the app in action can be seen in the gallery above. There's also a YouTube movie demonstrating SketchyPad in action.