While not DnD, I'm the GM for my groups Deathwatch games, which is a Warhammer 40K RPG where you play as Space Marines. While this does tend to dial down the craziness due to the sheer powerlevel of the characters, there are still some good stories. A personal favourite would be when our Black Templar decided to utterly level a house containing a rebel stubber position. Bringing up his Missile Launcher and loading a Krak Missile, he manages to roll a misfire. It should be cool though, since there is a 7 out of 10 chance that the missile is simply a dud. Of course, the player manages to roll a 9, causing the Krak Missile to explode inside the Missile Launchers tube. This leads to a chain reaction where all the Black Templars grenades cook off from the explosion, and he has to spend a fate point just to survive. After some deliberation, it was decided that while the Missile Launcher is now unusable, the Black Templar got lucky and the explosion only singed his armor and incinerated his tabard, leading to a very pissed of Black Templar for the rest of that mission.
Another good story was at the tail end of a mission where everyone had been very lucky and not had to spend any fate points, our Blood Angel and Space Wolf found themselves dining together with a rogue trader whom they had chartered transport with. Things went a bit sideways after a bit of bragging from both sides, and things ended with the two players spending all their fate points on an armwrestling contest that lasted for 3 hours, before the Blood Angel finally brought down the Space Wolf with such force that they cracked rogue traders dining table.
An example from when I was a player in a Dark Heresy game, my previous character had just died, and my new character, an adept from a shrine world, was going to be introduced. An imperial guard troop mistok me for a priest due to my character having an aquila tattoo on the forehead as well as wearing robes, and since priests are a combat class decided to drag me to the frontlines. Of course, once we got there things turned sour quickly with suicide bombing children decimating the guardsmen. My character, terrified as he was since he is not supposed to be in combat, attempted to take on the demeanor of a priest, and managed to trick the guardsmen into charging straight towards the enemy lines while my character could stay behind and find someplace to hide until the shooting stopped.