Check out solar powered attic fans like the Natural Light Energy Systems unit from http://www.greenbuildingsupply.com/All-Products/Energy-Water-Air/Natural-Light-Energy-Systems-Solar-Attic-Fan
Whole house fans are becoming a current trend in Southern California. The units have proven to be extremely helpful to quickly pull out the hot air of homes and cool the home for the evening. They are only intended to be used for short periods of time and will use less energy that AC units.
Attic fans do help but ridge vent cost nothing to operate and a 4 foot piece of ridge vent equal 72 square inches of ventilation it creates a convection effect by pulling cool air through the eaves and out through the roof vent and much more energy efficient system than a fan
It depends on when it’s operating.
This is a good article.