Trapdoor

Hatches are a new block type being added to Beta 1.6. They will function the same as doors, but are oriented such that they will be placed on a flat, horizontal surface. Like doors, they require a solid block next to them to be placed, and also do not allow water to pass through. Unlike doors, hatches only occupy a single block of space, and they open upwards. As signs are rumored to lose the ability to hold water, it is likely that this will become the replacement.