Pokemon Black and White were very well recieved by fans, I quite enjoyed Black myself. Something about not recognising a single one of the little critters put me off, but the strong upgrades over previous entries into the series kept me playing. Like in the past, Nintendo must have a third game in this Poke generation and given the titles of the last games, the next one must be Pokemon Grey.
But it's yet to be announced, yet to even be mentioned as far as I know – up until today, that is.
Melbourne IT Digital Brand Services, the same company that registered pokemonblackandwhite.com, has registed pokemongray.com, an indication that perhaps an official announcement is around the corner.
Content of Pokemon Grey is utter speculation at this point, but I wouldn't be surprised to learn that it someone took advantage of the 3DS.
