Rain

Rain is a feature activated by pressing F5 ingame in Classic. It will only fall where the sky isn't blocked, and currently has no effect on gameplay. Though not official, Rain may be modified to fall in certain biomes. A png for rain is in the coding for beta.

Media
To see a video of rainfall in Minecraft, click here: http://www.youtube.com/watch?v=JfimKE6D5HE