Going to give two in game, and 2 in life (one of which wasn't my own, but it was awesome).
In game: I was playing Halo 3 multiplayer, me and my brother were in Avalanche about half of the width of the map away from each other. He had a rocket launcher and I had a Spartan Laser. We were both aiming at each other and he got his rocket launched first, which was inexplicably on target despite the distance, instants before the rocket hit me my Spartan Laser went off and hit both him and the rocket directly, killing him and detonating the rocket. We had to watch it again on the replay to be absolutely sure that was in fact what happened.
Another Halo one, we have a custom game mode that we call H1N1 where one player is a incredibly fast zombie with high shields and the other players have only a random weapon and an energy saber (chiefly to parry the zombie with if he closes in on you). We usually play on Sandtrap. In practice this usually breaks down to 3 zombies fruitlessly chasing the last remaining player in a warthog that is ever so slightly faster than the zombies, leaving ambushes the only way to take them out.
This ambush went as follows: The player had just cleared a bump on the road, behind which one of the zombies had hidden, the zombie managed to get a blow in from beneath the warthog, sending it spinning into the air. While this was happening one of the other zombies leapt into the air, met it at the apex of its flight path, struck a blow with the energy saber causing it to explode in midair. For some spur of the moment coordination, it looked pretty damn cool.
Real life ones:
I was playing grounders with one of my younger brothers a number of years ago and running away from him on top of the monkey bars. I made a bit of a miscalculation and missed a bar with my foot, causing the foot to slip through inbetween them. As the foot slipped through, I hit my hip on the bar on the right which managed to flip me completely upside down and tumbling headfirst to the ground. I am not consciously aware of doing any of this, but somehow, in the middle of this I managed to grab hold of the bar mid fall and catch myself. Which was probably good, because you know, falling headfirst from 6 feet is rarely a healthy experience.
The last one happened to someone else, but was cool enough that I have to share it. I was working at the climbing center before a competition, putting the holds for routes onto the walls. There were 3 of us suspended up 30 feet up the wall with ropes, screwing holds into the wall. There's two main ways of getting stuff up to us, either using a rope and pulley mechanism to bring a basket of holds, wrenches or tape up to us (usually reserved for larger and heavier items), or someone on the ground just tossing it up to us. One of my coworkers on the wall needed some tape and called down for someone to toss her it. As someone went to find the tape and toss it to her, the third person on the wall saw an opportunity. Just as the tape left the hands of the person on the ground he unclipped himself from the wall, swung across the gym and snatched it out of the air just before she caught it
The amount of luck, timing and coordination required to make that work is so absurd that I wouldn't have believed it unless I saw it