High-Altitude Medical Guide http://www.high-altitude-medicine.com/
Provides current medical information on the prevention, recognition, and treatment of altitude illness, as well as other health issues affecting travelers to high mountainous regions of the world.
Wilderness Medical Society http://www.wms.org/
A membership organization of physicians, nurses, physician assistants, EMTs and other first responders concerned with the health and safety of individuals in the wilderness. Hosts several conferences a year.