Here's one:
What if Captain America awoke in a world where the Nazis won WWII.
The scene starts quite similarly to the third issue of Avengers where Captain America apeared, except we neve get a good look at The Avengers. Captain America begins to awake, as we hear talk of "the empire" and "Dr. Zola" from the Avengers. Finally, the camera pans up, and we see a perfect recreation of the scene where they realize it's Cap, except Giant Man and The Wasp are wearing all black with lab coats over their uniforms, Iron Man is wearing all black with an "SS" symbol on his chest, and Thor is wearing a full SS uniform with a cape and a black mask with a silver skull with red eyes on the face.
Cap freaks, tries to escape, and they subdue him. They tell him of his situation, and Cap basically tells them to go **** themselves. He's taken to a holding cell, but the submarine is atacked by an unseen force. Cap is rescued, and taken to the resistance headquarters.
There, the leader of the resistance, a mutant named Eric Lensherr, introduces him to the others. The resistance consists of:
Matt Murdock, a former lawyer who was blinded as a child when nazi soldiers beat him near to death after killing his mother, who was holding religious services for Jews and Jehova's Witnesses in the basement of the tenament building where they lived.
Peter Parker, a super powered teenager who escaped from the Hitler Youth program.
Frank Castle, who's wife and sons were killed by soldiers after Frank, a soldier himself, disobeyed orders.
Scott Summers, one of Eric's protiges and a master stratigest who posseses the ability to emit powerful energy beans from his eyes.
Pietro, Eric's son who posseses superhuman speed.
Victor Von Doom, a brilliant scientist who's home country of Latveria was wiped out by the nazis, and fled here to America only to see it conquered aswell.
Ben Grimm, the leader of the Yancy Street Gang, who now serve as members of the resistance.
Wilson Fisk, a former gang leader who now seaks to reclaim his power.
Namor, an Atlantian Prince who fought beside Cap in the war.
Dr. Strange, a mystic who hopes to fulfil his oath as sorcerer supreme to make the world a better place.
They, along with the few hundred Americans and people from other countries who wish to see things as they once were, are the resistance. And, Cap becomes their leader.
I've got all sorts of ideas for nazi versions of vasrious heroes and villains. Also, Proffesor X and Jean Grey would be used, along with many other psychics, as human datas prosesors and are used to counter the resistance's actions.