For the past couple of weeks, Pokexperto's webmaster, Melkor, has been posting B/W information on his twitter and website. However, today he has posted on his website information about the Legendaries and their types. He has also stated that there will be 156 new Pokémon, making it 155 Pokémon in the Isshu dex with Victini as #000. There will also be 3 event Pokémon, #647, #648, and #649 that you're able to receive from as-of-yet unknown events. Much like how Darkrai, Shaymin & Manaphy have been distributed.
Here, we have a list of disclosed Legendary Pokémon along with their National Dex # and Types.
New Legendary Dogs Trio - these are the new Legendary Dogs, but with different types.
* #638: Steel/Fighting Type Pokémon
* #639: Rock/Fighting Type Pokémon
* #640: Ground/Fighting Type Pokémon
Raijin Trio - The following we have what it seems like a Raijin trio, according to Pokexperto.
* #641: Flying Type Pokémon
* #642: Electric/Flying Type Pokémon
* #645: Ground/Flying Type Pokémon
The Dragon Trio - Two of these Dragons have already been revealed (ReshiRam & Zekrom) The third will probably star in the third version, and is based on an energy source as cold as ice instead of heat or electricity.
* #643: Reshiram - Fire/Dragon Type Pokémon
* #644: Zekrom - Electric/Dragon Type Pokémon
* #646: Ice/Dragon Type Pokémon
Event Pokémon Trio - These Pokémon will be distributed much like Darkrai, Shaymin & Manaphy were in the 4th Generation Games.
* #647: Water/Fighting Type Event Pokémon
* #648: Normal/Psychic Type Event Pokémon
* #649: Bug/Steel Type Event Pokémon
Source: Pokexperto.net pokestation.net