Ditto to most in this thread. Tried a lot of the free apps but the once that get the most mileage for me are Epocrates (not free but you can find a way to get hooked up if you try hard enough), Medscape (esp OCM), Medcalc, and Eponyms. The QxMD Heme Calc, Neph Calc, and Cardio Calc have a few extra equations that aren't in Medcalc as well, and are free.