Black and White are the most opposing game titles to date, so I'm thinking there will be plenty of version exclusives and differences. I thought of an "Exclusive" Ball, a ball that has a higher catch rate on Pokemon you have a better chance of getting in a specific game.
It works like this:
Lets say there are some Pokemon differences in White and Black:
In White, you can catch Zekrom but not Reshiram, and Solrocks appear much more commonly than Lunatones.
In Black, you can catch Reshiram but not Zekrom, and Lunatones appear much more commonly than Solrocks.
According to these conditions:
In White, the catch rate would be the best for Zekrom, and a smidge lower for Solrock.
In Black, the catch rate would be the best for Reshiram, and a smidge lower for Lunatone. In both games the catch rate would be the lowest at Pokemon like Generic Starting Bird and Generic Vendor Trash Critter that you are equally likely to find in both games.
This ball would be ideal for people that catch Pokemon to help friends with the different version out, or maybe for catching the legendaries.