The official Pokémon Japanese website has announced some new Wi-Fi events for those of you with HeartGold/SoulSilver.
From November 11th to November 23rd you can download a Mew. It will be level 5 and will have the Premier Ribbon. This Mew will then be available to Diamond/Pearl/Platinum (again Japan only) January 29th to February 11th.
From November 27th through January 11th you can download the Enigma Crystal. This item is to be taken to the Pewter City Museum which will activate the Soul Dew. This will allow you to battle either Latios (HeartGold) or Latias (SoulSilver).