The next Pokémon event is gearing up next month! Shiny versions of Entei, Raikou, and Suicune will be given away thoughout January (and early Feb) at GameStop. The event works for Diamond, Pearl, Platinum, Heartgold, and Soulsilver so if you have multiple games you can really stock up! Besides being shiny, they also know moves that they can't normally learn (for example they all have ExtremeSpeed). Each week is a different beast.
Jan. 3rd thru Jan. 9th - Shiny Raikou
Jan. 17th thru Jan. 23rd - Shiny Entei
Jan. 31st thru Feb. 6th - Shiny Suicune
You will need these guys once Black and White come out by the way. Without at least one of these to transfer over you cannot capture the new pokémon Zoroark. As with all DS events each is in a Cherish Ball and have a Classic Ribbon. All of the shinies, and Zoroark, will star in the next pokémon movie this spring!
*Update: Toys 'R us is also has an event coming up as well. Between Jan 30th and Feb 5th TRU will be giving away Ash's Pikachu. It's doesn't activate anything, but it does have Ash as the OT and knows moves that Ash's Pikachu knows in the show.
*Another Update: The Gamestop Shiny Beasts are now available via Wifi download throughout February! Full story here.