This escaped my attention earlier, but the Merck Manual is now available as an iOS app for iPad, iPhone, and iPod Touch. According to the app description:
The Merck Manual - Professional Edition has an easy-to-use interface for finding the right information quickly, wherever and whenever you need it (a Wi-Fi/Internet connection is not needed to access the content of the app). The app does not require visiting another website for registration, subscription or software downloads. The Merck Manual - Professional Edition is available for iPhone, iPod touch and iPad, and takes full advantage of the large iPad screen for displaying medical images, charts and figures.
The application is available in the App Store for $34.99.