I'm a third year medical student and I have used Epocrates, Diagnasorous, UptoDate for PDA, Five minute consult for various specialties, Surgical Recall for PDA. Epocrates is a must have drug reference in my opinion, it also has lab information and differential diagnosis information. UptoDate is really one of the authorities in medicine, although it's somewhat expensive. Five minute Consult software is very easy and quick to use and it has the essential information. Surgical Recall is very nice, because it's essentially the book, but it's much easier to carry the softwear on my PDA than to carry the big book in my coat pocket. Diagnasorous, is free (so is epocrates) and it's a quick and dirty way of coming up with differential diagnoses.
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