Hello Planet Minecraft, I wanted to tell everyone about the upcoming 1.4 update!

Here is a list of things you can look forward to:
Zombies infecting villagers, and baby villagers.
Baby Zombies!!! They never grow old, they are faster than other zombies, and they don't burn!
Some mobs(Zombies and Skeletons) will have armor and enchanted weapons!
More half-slabs!
You will be able to change the type of block that super-flat is made out of!
Blocks that can run singleplayer commands!(Intended for Adventure Mode)

The pre-release for this upcoming version has not been released yet, unfortunately.

For more information check out the minecraft wiki page: http://www.minecraftwiki.net/wiki/Upcoming_features