This is the power plants map. Here's the link for the Sources of Power, Solar, Wind, etc. maps. (Click and scroll over)
HT: Dr. Hazlett at the Climate + Energy Project first showed it to me.
Now Infrastructurist pulls it out. They write:
From the archives: We stumbled again across this great map from NPR showing the US electric grid in four distinct aspects. The coolest part is a visualization that includes every power plant in the country represented by how much electricity it generates. (NPR)