Scott Manley's reusable space program was an epic series that involved multiple space stations across the Kerbin system, as well mining operations on multiple planets/moons. And he kept to his reusable program promise for an extremely long time, until a minor failure caused a part to break.
In a similar vein, his Interstellar Quest series, which has (as of 08/03/14) been going for longer, and achieved far more... in career mode!
The heroic-sounding music that plays at the main menu.
Since we talk music, the songs that play when the player reaches the 70Km barrier. It basically lets you know that you've reached Space. Awesome, indeed.
Though most of what he does is usually in the Funny end of the spectrum, Danny2462 can, and does, pull off some awesome stunts from time to time. Two of the best ones are probably getting a kerbal to the Mun without a spaceship (it had run out of fuel in orbit) and landing on the Mun on the next flight, all with the most basic parts that a single flight's research can afford you.
"But I still want to do science on the Mun... though I only have basic parts... Who cares! I'm going there anyway!"
Giving Kerbin a third moon by capturing a passing asteroid. Taken Up to Eleven if you then grab a fourth. And a fifth. And...