You should check
this page out, it lists most of the previous preorder gifts, though it skips a few.
Anyway, the last few Pokemon titles have had next to no preorder gifts, or just plain disappointing ones. Ruby & Sapphire buyers got collectable coins with holographic images of Groudon & Kyogre. Apparently with FR/LG they gave you a freakin'
messenger bag with the game's logo on it, the D/P/Pl games all had figurines (though only Japan got the cool Dialga/Palkia ones), and the HG/SS games offered the same.
B/W? Japan got Sound Drop keychains with the cries of Zekrom/Reshiram, which are pretty cool, and America got... well, at Target you got a set of postcard-sized pics with art from Gen 5 (which is much cooler than it sounds), ToysRUs gave out large wall clings of the Legendaries, but most other places only offered things like discounts on the strategy guides. I suppose the true bonus for B/W was being able to get Victini via wifi from Nintendo for the first month.
B/W2 was even worse, with Gamestop claiming that their Spot Pass download of Keldeo
was their pre-order bonus, though anybody walking by could DL him. I guess again that the true gift was Genesect via WFC.
I'm hoping that we actually get a gift this time around, but given Gen 5's significant lack, I'm not holding my breath.