So, there have already been two snapshots released today, the second being a huge bugfix from the first. This one adds things like waves of zombies sieging villages, villagers reproducing to make up for the deaths overnight, increased world height, and light sources that can be turned on and off with redstone!
I don't have a video yet, but I should have one up in just a few hours showing off some of this cool stuff. Have you found anything interesting in the snapshot I missed?
More information and the official download can be found here