The IIHS is run by insurance companies, who have a strong interest in saving money by saving lives. IIHS is by far the more useful of the two American crashtesting agencies. As with any crashtest, you should also be aware that any test result means only that a vehicle gives good or bad front and side crash protection in a collision with a solid object such as a lamppost, or a vehicle of similar weight. In actual road smashes the driver of a smaller (lighter) car is far more likely to die than the driver of the larger (heavier) vehicle it collides with.
The American government transport department (NHTSA) does crashtests that use an obsolete testing method. It's better than nothing, but the other American testing agency, IIHS, does superior tests.
IIHS also publishes a good list of the types of cars in which people died during real-life accidents.