The last stand at D6, at the end of the game. Gunning down Red troops, whilst constantly falling back to more fortified lines, eventually going to town on them with a home made gatling gun. Granted, you get your ass kicked in the end, but it's still very awesome.
Pulling off the Shadow Ranger achievement, with a minimum of blood spilled - that of the final target in the game, the flamethrower trooper at D6. You'll have either avoided or knocked out every single human opponent in the game, including the Reds on the train and at Red Square (both groups can be fought hand-to-hand, if you have medkits and a bit of luck), and getting this achievement almost guarantees the Redemption ending.
The Nazis holding off a MASSIVE Red Zerg Rush in the Faction Pack DLC.