Achieved depending on how you choose to play the game.
Over 3 million views! Thanks for watching!
Edit (25/9/08) - I'm getting tired of the 'what's the difference' and 'there is no difference' remarks regarding Endings 2 and 3. Anyone with eyes can see that they are visually identical, however (as stated in the video between 2 and 3) there is a difference in the tone of narration, 2 is angry while 3 is sad. Anyone who is not deaf or does not have broken speakers should be able to pick up on this, otherwise you're lost! Ok fine this is a small difference and the game writers could have probably put in more effort to distinguish them more. Nevertheless they are still different endings in their own right because they have been achieved by playing Bioshock in a different way. If you get the sad ending (Ending 3) then you saved some little sisters but probably killed a few out of curiosity, so the narrator is sad that you gave in to temptation. But if you get the angry voice ending (Ending 2) you have probably rampaged your way through the game killing every little sister you came across with a big smile on your face as you plan which plasmid you'll get next, so the narrator is angry that you have been so selfish and greedy.
Edit 11/2/2010 - Over 1 million views - thanks for watching!