Just a heads up, Nintendo World is not doing anything for the release. I keep up with them for merchandise, and they say that Toys R Us bought the right to have the release party or something.
Anyway, if you pre-ordered your game at TRU (see the TRU site for specific stores) then you can attend their events for some giveaways. Most TRUs will be giving out shirts with ho-oh on one side and lugia on the other, with the game logos on the sleeves. Each store only gets about 40 though, so show up early. Apparently you also have to compete in some battles to win the shirts, but the details are unclear.
Some stores are offering a deal where you can pre-order the game and you get a DS basics set that includes a nice screen cleaner (Black with gold and silver ho-ohs and lugias) as well as two game cases and two HGSS styluses. I have them, they're pretty neat.
Lots of little giveaways too, like sticker sheets and such.
I sort of wish I didn't live in Canada.