This might be old news, but it was new to me as of last week. ConEd Solutions offers a Green Power option to all ConEd customers. For an additional $0.005 per kilowatt hour, customers can purchase electricity from renewable sources. In the case of ConEd, the sources are 25% Wind, 75% small hydroelectric. ConEd customers can learn more and sign up for green power at ConEd Solutions.
While the ConEd Solutions web site offers a fair amount of information, I found this essay by Walter Simpson to be a bit more informative. At the bottom of the page, he provides several links to other green energy providers around the state.