Here'a pic of a ridge vent. Supposedly extends the life of roofing materials and lowers temp in the attic, therefore in the house as well.
They basically cut a slot at the peak of your roof (for the entire length)and install the plastic vent over the slot. It is then covered with matching shingle to blend in. Cobra is the brand I've used. BTW, modern ridge vent systems can look better than the one pictured below.
