Indiana Jones Hat: whip 120 snakes or spiders in the dream to get gold. When you will get a gold medal, you will receive the Hat.
How to unlock videos:
Behind the Scenes: 1000 Precursor Orbs
Concept Art: 700 Precursor Orbs
E3 2005 Trailer: 600 Precursor Orbs
Game in Construction: 900 Precursor Orbs
Intro Animatic: 800 Precursor Orbs