Also, I now have a picture of the bonus:
(Credit to Pokemon Aus for the image!) Gametraders is selling Pokemon Black & White for $69.95 each and when you pre-order, you'll receive a Pikachu 30cm plush. (Presumed bootleg, unfortunately.)
At EB games, they are $68 each and the pre-order bonus is Pokemon Black & White DS kit.
JB Hi-Fi is selling the games for $59 and you'll recieve Reshiram and Zekrom DS case when you pre-order.
We still don't know about bonuses (if any) from shops such as GAME or K-mart. The choice is up to you! As for me, I already pre-ordered Pokemon Black from EB Games this morning! :3
Information from Pokemon Aus: http://www.pokemonaus.com/