Radiopaedia.org, that has been offering radiology teaching files on the iPhone for a while now, has recently updated its offering with an HD version for the iPad. It has high-resolution images and additionally includes multiple scrollable stacks with up to 350 images per case and links to additional online cases. The first volume is now available. The only downside is that it is not a universal app, meaning that if you have previously bought the iPhone versions, you have to pay again for getting them on your iPad, which is a bit of a let-down. At $5.99 USD a volume it does add up. On the other hand, you get high quality cases and images and the authors promise that all proceeds go towards the maintenance and further development of Radiopaedia.org.
iTunes link: Radiopaedia Vol 6: Head and Neck Radiology Teaching File HD