Disk Galaxy Formation Simulation
Pretty fantastic cosmological simulation from the Big Bang to the formation of a Disk Galaxy with "rich merging" and plenty of collisions from NASA's N-body shop (makers of quality galaxies). Slightly hypnotic to watch and would be much better with a nice soundtrack (and a drink!) to accompany it imho, but cool nonetheless.
Likey? You can also check out a video simulation of a Milky Way like galaxy forming.
Both are full screen, darkened room kind-of-ones to watch.
The Disk Galaxy simulation was NASA's APOD for 17 July 2012.