There are so many Plasma Vs LCD threads on internet and I don't want to start another one.
So, here are power consumption facts
(Work time:5.2hrs/day, Stand-by:18.8hrs/day, 365 days/year, 11.55 cents per kwh).
Cost per year:
Worst case plasma 50": $117.94
Best case plasma 50": $36.27
Worst case LCD 47": $61.78
Best case LCD 47": $39.74
Source
Choose wisely and save massively :D