Wind turbines generate electricity without generating carbon dioxide or any other greenhouse gasses, the fuel is cost free, and it will never run out.
Modern wind turbines pay back the energy used in manufacture within 2-10 months depending on the wind speed of the site and the type of turbine used. Most turbines have a life expectancy of at least 24 times the energy used in manufacture and installation.
At the end of a wind farm's working life, the area can be restored at low financial and environmental costs. The footprint of a utility-sized wind turbine powering more than 2000 homes, can be as little as 16 feet (five metres) in diameter, with all the land around it being available for agriculture.
Furthermore, for every gigawatt of fossil fuel fired electricity generation capacity displaces by an equivalent amount of renewable energy electricity, carbon emissions are around 0.7MtC to 1.5MtC lower.
Ref: Energy from wind: an explanation of terms http://www.berr.gov.uk/files/file17817.pdf
Danish Wind Energy Association: http://www.windpower.org/en/tour/env/enpaybk.htm
Energy White Paper: Meeting the Energy Challenge http://www.berr.gov.uk/files/file39569.pdf (p143)