There are also plenty of a-ehm "free" (in the Yaaaargh! sense) medical books out there. I've some on my N900, namely two Italian manuals of clinical therapy, and in English one compendium of psychotherapy, the dsm-iv, a textbook of physical diagnosis, "the" textbook of pharmacology, and "the" textbook of clinical medicine.
They are better than any app imho. PM for details.