Through Sept 2012, Wind was 3.3% of electricity generation, Nat Gas 31.4%, Coal 36.5%, Nuclear 18.8%, Hydro 7%. Wind generation grew 17.7% since the first 9 months of 2011 & 10-yr CAGR is 28.3%; NG grew 26%. 

Source: http://www.eia.gov/electricity/monthly/ modified to combine Table 1-1 w/ 1-1a