The single best 'silver bullet' moment in the history of my gaming occurred in a campaign I was in in college.
One of the main plot threads of the story had coalesced around this civil revolt against an evil queen and her ruthless minions, eventually culminating in a siege of her fortress like capital city by an alliance of rebel forces lead by the party's Ranger - many of which were forest dwellers. The allies had attacked the fortresses strong point, owing to the fact that it offered the speediest access to the Queen's palace, hoping to finish the battle quickly. Unfortunately, the Queen had anticipated this and had arranged for the strong point to seem much more lightly defended than it actually was, baiting the allies into this very action as a trap. She had arranged all her most elite forces hidden in the approaches to this strong point, including her loyal wizards. For the allies, the key to the battle lay in their Treant units, which could batter through the fortresses walls. The treants breached the outer wall, and the rebel army began to pour through the breach. At that moment, the queen sprung her trap. The rebels found themselves trapped between the outer and inner walls, and surrounded on all sides by the queen's most elite units. Worse, the queen's wizard allies had conjured fire elementals which now bore down on the Treant units, threatening to do serious harm to the most important unit in the rebel army. The PC's were momentarily frozen with indecision and worry, and the battle seemed hung in the balance.
Several of the players were actually playing some of their higher level henchmen for this battle, with their main PC's elsewhere. One of the players scanned the relatively unfamiliar character sheet, looking for a solution. And at that moment, he realized that the entire campaign had turned on a seemingly unimportant decision he had made months earlier.
It was usual when distributing treasure to give your henchmen magic items which had little utility to your main PC. By the rules, this bolstered your henchmen's loyalty scores regardless of the quality or utility of the treasure. Months earlier we had found a particularly worthless seeming magic item, and since no one wanted it, it was duly assigned almost at random to one of the henchmen that could use it - in this case a Halfling thief that was high enough level to utilize wands.
That Halfling thief now stood in the middle of the main boulevard, with the elite forces of the Queen bearing down in all directions, flights of arrows cutting down the lead units of the rebel army, fireballs bursting round about, and a unit of fire elementals threatening to turn the tide of the battle. The player controlling the Halfling thief announced, "I pull from my pack my Wand of Fire Extinguishing, and target the nearest fire elemental."