If you want to spoil it for yourself, you can find it but yes the ending for Halo 3
has been put online. Personally, I'm avoiding it as I'd like to play the through the game but if you are so inclined you can find it for yourself. Don't know how long it'll be up on tube but hey knock yourself out if you want to spoil it. I did find it but only caught a tiny bit of it.
Saw the news on Kotaku