Drug reference that includes drug guide, Pill ID and Pill pictures, formula information and drug interaction checker. On this site you can download the free version of Epocrates or purchase versions with more advanced features.
Mediquations has over 232 formulas and scores, and supports US and SI units of measure. It is consistently rated very high for its overall accuracy and usefulness. The app can be purchased for around $5.00 from iTunes or the Android Market.
The Antidote app is a succinct resource designed for quick access to indications and dosing regimens for a variety of medications and antidotes used for common poisonings encountered by emergency care providers. Cost: Free; Device availability: iPhone/iPad and Android devices