In the upcoming Sequel to Pokemon: The first Movie; We get our first glimpse of one of the new (and Powerful) Pokemon, Luiga. I am unsure if he will be named this in the new movie. You can also find Houhou, the fourth legendary bird, which Ash saw in one of the first episodes of Pokemon, flying over the rainbow. There are also at least 2 new types of Pokemon. Evil and Metal. In Gold and Silver, (as with red, blue and yellow) You start off with one of 3 Pokemon. Either a plant type, a fire type, or a water type (Sorry folks, they aren't Bulbasaur, Charmander or Squirtle). You also have a rival again (not Gary), but it turns out his pokemon are stolen! Next, not only are there new items (skateboard[?], pokedex/wrist watch/cellular phone) but there are also new forms of old pokemon such as the eevee evolutions. Eevee has 2 new evolutions. A psychic and an evil form. Pikachu, Jigglypuff and Clefairy also have pre-evolved forms. Koga from Pokemon Red/Blue/Yellow turns out to be in the Elite four, so his daughter(?) took over the gym. The game is also real time so there is night and day, Monday through Sunday. Just like in Red/Blue/Yellow, you can't find certain pokemon in the game. In gold, you can only get Ekans/Arbok in the game corner, and you can't find Vulpix, Ninetales, Meowth or Persian. In Silver you can only get Sandshrew/Sandslash in the game corner and you can't find Growlithe, Arcanine, Mankey or Primape. Finally, (this is a long list) You can't get Bulbasaur, Ivysaur, Venusaur, Charmander, Charmeleon, Charizard, Squirtle, Wartortle, Blastoise, Omanyte, Omastar, Kabuto, Kabutops, Articuno, Zapdos, Moltres, Mewtwo or Mew in either version. To get them, you must use a new feature. The Time Machine which is in pokemon centers. This allows you to trade a pokemon from Red/Blue/Yellow to Gold/Silver without trading anything back. Another feature is with trading pokemon. You remember the pokemon you could get only through trades right? (Machamp, Gengar, Alakazam and Golem) Well, in G/S for some pokemon, you now have to attach an Item to make them evolve. As with Pokemon Red/Blue to Yellow, Gold Version has different images for pokemon than yellow just like these two Flareon
As the details become more clear, I will fix up this news area and when Gold and Silver DO come out, I will get all the information to you.
Pictures of the New Pokemon in Gold Version