The mobile medical application blog iMedicalApps has complied a list of the top 20 iOS apps for health-care professionals. Its number one recommendation is Medscape (link to App Store):
Many use Medscape as a simple drug reference tool, but its true value is in the disease and condition clinical references it provides. This is highlighted by some of the below pictures where we show the type of content provided when reading about an AAA. The Medscape app is actually a mini-textbook packed with protocols for disease pathologies. It's not as detailed as the famous Pocket Medicine Red Book -- but it does more than an adequate job of providing clinical pearls from the most common to less common pathologies.
The list appears to be fairly comprehensive, with the only downside being that the list is split into 20 pages (one app per page).
Image is Medscape screen capture