Benito Juárez, one of the most revered Mexican presidents, was about to be executed along with his whole cabinet by a traitor squad, when his friend Guillermo Prieto, then Minister of Finance, barged in. Prieto then put himself between the firing squad and Juárez and began a passionate speech with the words: "Put down those weapons! Put them down! Brave men don't murder! You are all brave men, and brave men don't murder. You are Mexicans! This is our representative for the law and our country! Lay down those weapons! Do you want to spill blood? Takemineinstead!". He spoke until the firing squad retreated after he convinced them to spare their honor as soldiers and not betray the republic.
King John III Sobieski of Poland and the Holy League at the Siege of Vienna in 1683. The Ottoman forces have had the city under siege for month and have finally managed to place the underground charges to breach the walls when 30,000 Polish heavy cavalry, led by the King himself and his famed elite Winged Hussars, show up, perform the largest cavalry charge in human history straight into the Ottoman lines, rout the Turks, and save the city. The Pope declared Sobieski the savior of Western civilization.
Against all probability, infamously bumbling mayor of London Boris Johnson recently pulled one of these when he intervened to stop a woman being attacked whilst out on his bicycle. Makesyouwonder...
The 442nd Regimental Combat Team, rescuing the 1st Battalion, 141st Infantry in the Vosges Mountains on October 30th, 1944.
Ironically enough the rescue resulted in MORE casualties then there would have been if the Hero Moment didn't happen.
More irony is that the 442nd was made up entirely of Japanese-American enlisted men. Most of the men had family sent off to the internment camps, and they still fought for their country with a heroism that made the 442nd the most highly-decorated regiment in the history of the US military.
Daniel Inouye, the late Senator of Hawaii and former President Pro Tempore, led the 442nd in that rescue. He took a shot to the stomach, destroyed one machine gun nest, destroyed the next with his men, had his arm blown off, pried the live grenade from his (dead) right hand, destroyed the last nest, finished off the last German soldier with a one-handed burst from his Thompson SMG, was hit in the leg, and tumbled down to the bottom of the hill unconscious. For his actions, Inouye was awarded the Medal of Honor. The best part? He was one of twenty-one soldiers in the 442nd who were awarded the Medal of Honor.
The NATO air forces saving the Libyan rebels, just as their base of operations was about to be invaded by Gadaffi's forces.
Given the aftermath, this unfortunately also falls under Nice Job Breaking It, Hero, as the rebels turned out to be fanatical Islamsists who, instead of trying Gadaffi openly as Saddam Hussein had been tried, settled for apparently sodomizing him with a sharp object and then executing him. A little while later, they did something similar to the American Ambassador and several others, and trashed the Embassy.
Both Senator Leticia Van De Putte and the citizens of Texas did this for Wendy Davis, after her 13 hour filibuster of an abortion bill in a special session of the Senate. Right as the Republican controlled Senate was moving to vote to end her filibuster, Senator Van De Putte, who had left her father's funeral to be there, delivered a parliamentary inquiry: "At what point must a female senator raise her hand or her voice to be recognized over a male senator in the room?" The crowd erupted into a solid twenty minutes of cheering, destroying the ability to call order and the roll and pushing the session past its legal end time.