Grand Theft Scratchy
Banned
So I guess my choices are predictable as I'm a big fan of the Deus Ex series and older GTA games. At 1:05 of the Deus Ex anniversary trailer, I like the reference to the Helios ending of Invisible War in the background (the virtual Statue of Liberty) where world peace is attained by uniting everyone under a single powerful, all-knowing A.I. Usually I'm not a fan of animated trailers but this one was pretty cool. As for the Grand Theft Auto: San Andreas tribute trailer, I feel it is actually better than the official anniversary trailer released by Rockstar, showing a lot of the best parts of the game.
Anyway, I'm sure there are more anniversary trailers worth posting so feel free to share your favorites, official or fan-made.