Metro 2033 - the good ending.
How to get this ending:
The game gives you karma points for certain actions. If you have enough points by the end of the game, you get the good ending. It's pretty easy - all you need to do is explore the levels, talk to people, use stealth instead of fighting and act "good" when given an opportunity.
This video shows how to get all the moral points:
http://www.youtube.com/watch?v=k4QHUadMVgw
