Air Vent 18-in Dia Electric Gable Vent Fan in the Gable Vent Fans department at Lowes.com
iLiving - 24" Wall Mounted Exhaust Fan - Automatic Shutter - Variable Speed - Vent Fan For Home Attic, Shed, or Garage Ventilation, 4244 CFM, 6200 SQF Coverage Area (Power Cord Not Included) - - Amazon.com
Panasonic FV-04VE1 WhisperComfort ERV (Energy Recovery Ventilator), Ventilation Fan, Balanced Air Solution, Extremely Quiet, Long Lasting, Easy to Install, Code Compliant, Energy Star Certified, White - Bathroom Fans - Amazon.com
Using cheap junkyard car parts to make a solar-powered attic ventilator
Suncourt Inductor 4 in. Corded In-Line Duct Fan DB204C - The Home Depot