I am an infectious diseases physician and since my medical school days have always found the Merck Manual to be the best (and most concise) medical reference. In anticipation of a medical relief mission to Haiti last year, I downloaded Merck Manual because I wanted a full medical reference that would not require an internet connection once on my iPhone. This app proved invaluable the few times that I needed to read about some conditions (and treatments) that I was not familiar with and is an excellent general resource. Besides use for medical students, physicians in training, and other health care workers, I highly recommend it for anyone doing overseas relief work and needing an excellent medical reference.
WashingtonMD about Merck Manual Professional, v1.2