http://www.minecraftforum.net/news/230-19-is-out/

1.9 includes:

New mobs
Villager
Magma Cube
Snow Golem
Mooshroom
Blaze
New blocks
Netherrack Bricks
Netherrack Stairs
Netherrack Fence
Lily Pad
New items
Blaze Rod
Ghast Tear
Nether Wart
Gold Nugget
New generated structures
Nether Ruins
New Bugs
Biome tinting is too harsh between regular water and swamp water, rather than blending.
Can no longer jump repeatedly by holding a key
Snow golems do not take fall damage