iTriage Health offers lots of useful tools including a symptom checker, medical facility locator, first aid instructions, and more.

WebMD for Android tons of useful tools including a prescription pill identifier, offline first aid tips for common emergencies, voice search functionality, and more.

CPR•Choking Covers first aid techniques for handling two common and deadly emergencies. Folks who study and review the content will be prepared to handle these situations should the need arise.

Epocrates Popular with medical professionals, this app features a massive drug reference section including drug interaction warnings, dosages, black box warnings, and more.

Medscape Another app preferred by pros, Medscape offers some of the same features as Epocrates but also includes an offline clinical reference section.