Not much is known about it other than what is in the trailer.
HGSS Date! 12/31/2009
Games Heartgold and Soulsilver will be available March 14, 2010 in the US! Mark it now and buy it then.
New Hyperbeam!?! 11/28/2009
This has not yet been proven to me but I hear the move Hyperbeam in Heartgold and Soulsilver will be upgraded in the looks department. Still will have the same stats I suppose but looks different than all past games.
Tsunekaz Ishihara, president and CEO of The Pokémon Company, was interviewed in a recent issue of Famitsu magazine. He gave the following statement at the end of the interview:

I can't give any details at the moment, but we're working on a new Wii game. We should be able to announce something before long. -- Tsunekaz Ishihara

It is unknown if this will be another WiiWare game, such as Pokémon Rumble, or a battle simulation game, such as Pokémon Battle Revolution. So far, there has only been one Pokémon game for the Wii sold on discs while there have been five WiiWare games released, only one of which has been available to users of non-Japanese Wii systems.

-Content from Bulbapedia
  • Heavy Ball that does great at catching heavy pokemon.

    Elm's Lab has an upstairs level, where the professor and his family live, his old house being occupied by Kotone/Hibiki and her/his family.

    New Moon Ball which catches pokemon that evolve with a moon stone.
  • Maps have been remade to match the design style used in Diamond, Pearl, and Platinum.
  • The Battle Tower west of Olivine City, introduced in Pokémon Crystal, returns, bringing with it the Battle Frontier introduced in Platinum.
  • Two new routes, Route 47 and Route 48, are introduced near Cianwood City. They lead to a new Safari Zone.

    Johto's Pokédex has been redesigned.
  • Mt. Silver is much bigger and Viridian Forest is not cut down.
  • Cerulean Cave and the Seafoam Islands remain as they were in Generation III (though Blaine still takes part of the Seafoam Islands), allowing the legendary Pokémon that live inside them to be battled.

    The PokéGear has been redesigned. There are a range of skins that can be used and changed at the player's will.

    Moltres, formerly found in Victory Road and Mt. Ember, can be found in Mt. Silver.
  • The Fighting Dojo in Saffron City takes a role similar to Sinnoh's Battleground.

    The Magnet Train's tracks can be seen overground in locations such as Route 32.
    The english logos for Heartgold and Soulsilver have arrived. The games are scheduled to premier in the US and Europe in the spring of 2010.
    Pokemon: Rumble 09/05/2009
    There's a new game out for WiiWare called Pokemon: Rumble! It is, in a nut-shell, a battling game were you simply fight over and over again. You can have tag battles, single battles, and may more types too. Coming soon!
    The new movie Arceus and the Jewel of Life is coming and we are preparing. The movie is the conclusion to the climatic battle between Palkia, Dialga, and Giratina with Arceus delivering the finale. You'll have to watch it to see what happens to Ash, Pikachu, Team Rocket..., Pokemon..., and the world! 

    Arceus and the Jewel of Life: Coming soon!
    (The video is the official trailer.)
    Heartgold and Soulsilver are to release in the US and Europe In spring of 2010!
    Above is a screenshot from the new games and below the PokeWalker. It is a devise that comes with all HG&SS games.
    There will be a trio of Pokemon: Mystery Dungeon's. They are Keep Going! Blazing Adventure Squad!, Go For It!Adventure Squad!, and Let's Go! Adventure Squad!, all to release in the US soon. The games are centered around Arceus and differ by starting pokemon. Not much else is known at this time. Keep posted :D