Do you mean average for a trip or top rate?

Average depends very strongly on particular conditions of the line taken. For example, average distance between stops: in Paris Metro 550 m, in St. Petersburg Metro 1850 m. In Paris lots of 75 m tight curves, in St. Petersburg minimum curvature is 600 m. Some lines have steep sections, others are flat. Technologies introduce difference as well.

I only have data for Moscow Metro (as of 2007). The average power consumption here is 52 W*h per t*km. An average train is about 305 tons, so it is 15.86 kW*h/km.

Top rates you can find for different rolling stock models:
http://en.wikipedia.org/wiki/R142_%2..._Subway_car%29
http://en.wikipedia.org/wiki/E1_Series_Shinkansen
http://en.wikipedia.org/wiki/81-717/714
and so on... See "power outut" in the information box.