The most complete pressure point charts are on AcupunctureProducts. The site divides the pressure points by the organs each is associated with. Martial artists use a different pressure point chart that focus on only the 45 or so points that affect combat.
Pressure points have two main uses. As clusters of nerves, they can cause intense pain or weaken an area of the body. In medicine, they can help restore the health of an organ. Eastern philosophy has it that a person's health is based on how strong their energy lines are and pressure points play a huge role in keeping them operating well.