As many of you probably know, the next version of Minecraft is available for testing.
Prerelease 5:
Client: http://assets.minecraft.net/1_9-pre5/minecraft.jar
Server: http://assets.minecraft.net/1_9-pre5...aft_server.jar
Installation:
Put minecraft.jar in %APPDATA%/.minecraft/bin (make sure to make a backup of your old minecraft.jar if you have any mods)
You can check the changelog for this update here.