"VICTORIA'S wind farms are saving more than 250,000 tonnes of greenhouse gas emissions every year, a new report shows.
...
They saved more than 250,000 tonnes of greenhouse gas emissions - the equivalent of taking 60,000 cars off the state's roads.
...
Each megawatt hour of wind energy generated in Victoria currently avoids producing on average one tonne of greenhouse emissions."
http://www.news.com.au/story/0,10117,19732572-421,00.html
[linked from junkscience]

In regards to the US:
"The Energy Information Administration (EIA) reports that the U.S. nuclear industry generated 788,556 million kilowatt hours of electricity in 2004"
http://www.eia.doe.gov/cneaf/nuclear/page/nuc_generation/gensum.html

788,556 million kilowatt hours equals 788.5 million megawatt hours, so using above metric, this saves 788,556,000 tonnes [.79 billion tonnes] of greenhouse gas emissions and equivalent of taking 189,253,440 cars off the roads.

{note: "The United States led the world in nuclear electric power generation in 2003 with 764 billion kilowatthours or 8.0 quadrillion Btu (Tables 2.7 and F.7). France was second with 419 billion kilowatthours or 4.3 quadrillion Btu and Japan ranked third with 237 billion kilowatthours or 2.4 quadrillion Btu. In 2003, these three countries generated 56 percent of the world's nuclear electric power ." http://www.eia.doe.gov/iea/overview.html } [of course as percentage of total power needed (or per captia basis) the US lags the developed world in regards to nuclear power electrical generation]

And US wind generation:
[note: Since wind speed is not constant, a wind generator's annual energy production is never as much as its nameplate rating multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. A well-sited wind generator will have a capacity factor of as much as 35%. When comparing the size of wind turbine plants to fueled power plants, it is important to note that 1000 kW of wind-turbine potential power would be expected to produce as much energy in a year as approximately 350 kW of fuel-fired generation. http://en.wikipedia.org/wiki/Wind_power ]

In US wind produces "11.2 billion kilowatt-hours of electricity annually"
http://www.memagazine.org/backissues/jan03/features/winding/winding.html

So that's 11.2 million megawatt hours,that saves 11,200,000 tonnes [.01 billion tonnes] of greenhouse gas emissions and equivalent of taking 2,688,000 cars off the roads.

Oh, btw, Germany is world leader in wind generation it produces [or at least has the capacity] of twice US wind generators [ therefore very roughly saving .2 billion tonnes of greenhouse gas emissions and equivalent of taking and around 5 million cars off the roads.
[refer to http://en.wikipedia.org/wiki/Wind_power ]