Pokemon Emerald

Emerald is out now in Japan. It's like the expansion to Ruby/Sapphire, just like Yellow and Crystal were to R/B and G/S. It comes with Rayquaza on the box and it seems that you will be able to catch Deoxys in it, maybe as a Legendary? Looks like you'll still be facing off against Teams Magma and Aqua too.

The Double Battles will make a reappearance too, but this time they might be totally different Trainers that team up when you battle one of them.
Pokemon Emerald features the pre-battle Pokemon animations previously used by Crystal. Let's just hope they put in the day/night feature, mobile phone and Pokemon Radio too.

Later: Apparently they just keep the 'daylight' on all the time, even at night. Pity....it would have been good to see an enhanced graphical version of the night feature.