Recently a number of people have come looking for good quality iPad templates and GUI elements for quick mock-ups. Here is short list of great free resources for designing layouts, wireframes and mock-ups with photoshop and illustrator.
This first link to teehanlax.com has a great illustrator file with sketchy elements. If you're a regular of web devil then you'll know that we prefer the sketchy look - it conveys the message of the layout and makes it obvious that style is not implied.
This next link to kaishinlab.com has a great vector of just the iPad product.
And finally a link to a photoshop file that has GUI elements for mock-ups with a "realistic" look of the actual OS.
If you found this useful then you'll probably like this previous Web Devil post about how to check your website for iPad compatibility using iPad emulators.
mobile website design using device specific viewport sizes.