Excuse me for being an evil super-villain, but actually, just thinking about this one, probably the most *effective* super power would be the ability to kill anyone, anywhere on earth, simply by willing it.
You could demonstrate your power to the world by getting in contact with someone heading for the Dignitas clinic in Switzerland - ie someone who has already chosen to die and therefore has nothing to lose by participating. At the appointed time, with impartial observers in place to watch both you, sat at home in the UK or USA, and your volunteer "target", 100's of miles away in the Dignitas clinic, you could wish him dead and *bing*, he'd be dead.
You would be God. Only with a real, physical presence on earth.
Want to end the Israeli offensive in Gaza? No problem. "Mister Netanyahu, call off your troops or I will decide that you die.".....