There are already plenty of upcoming opportunities for you to go to stores and download new Pokemon for HeartGold, SoulSilver, Diamond and Pearl. According to reports claimed to originate from GameStop employees with access to the promotional materials for those events, there is still one more that has yet to be announced. In the underworld of retail Pokemon data distribution events, news travels fast.
According to the reports, GameStop will offer Celebi downloads from February 27 through March 7. This is noteworthy enough, as Celebi is exceptionally rare, but this particular Celebi activates a time-travel event when encountered in HeartGold and SoulSilver, which can't be accessed any other way. Having this Celebi and transferring it into the upcoming Pokemon Black or White will also allow you to get a Zorua, one of the new Pokemon in that game.
So, in conclusion, we just wrote a whole bunch about a Pokemon distribution event that hasn't been announced. Didn't expect to do that today.