Plastic vents are a common material for most new roofs and they do the trick. However there are some drawbacks; raccoons have been known to be able to rip the tops off of plastic vents so they can provide a home for themselves in your attic space! The metal vents shown in this picture eliminate that possibility.

The larger vents shown are part of the 'Ventilation Maximum' series. Each one these vents can exhaust up to 1,200 sq. ft. of attic space. They are often considered the top vents in the market. This particular style of vent system is designed for vaulted indoor ceilings.