For a panenka penalty kick, instead of smashing or placing the ball into the corner on a penalty kick, the player fearlessly chips the ball into the net, usually right down the middle. Here's how it's done - watch how Zlatan Ibrahimovic calmly chips the ball into the back of the net. Look at how focused Ibrahimovic is before he strikes the ball.
From the Wikipedia entry for Antonin Paneka - who originated this gutsy type of penalty kick and whose name represents the kick:
With the score 4-3, Panenka stepped up to take the fifth and final Czechoslovakian penalty, to win the match. Despite the immense pressure, he fooled German goalkeeper Sepp Maier into diving for a save, before coolly chipping the ball straight down the middle and into the net. The sheer cheek of the goal led a watching French journalist to dub Panenka "a poet", and to this day his winning kick is one of the most famous ever, making Panenka's synonymous with that particular style of penalty kick.
And here's Pirlo taking a penalty kick and pulling off a clever panenka and the oringinal Antonin Paneka showing you how it's done:
And here's Jozy Altidore's very gutsy panenka penalty kick versus Panama. If you chip the ball down the middle and it doesn't work...especially when it's a World Cup qualifier, I'm sure Bruce Arena would have been pretty upset at Altidore. But it worked!
I'd also say that if you take a lot of penalty kicks for your team, then it is good to vary the types of penalty kicks you take, so the keeper doesn't know which way you're going to go.
Finally, there's the greatest of all panenka penalty kicks. That of course would be Zidane's panenka penalty in the World Cup final for France!