There are lots of Pokemon cards and Bakugan balls/cubes, so you can spend a fortune on them if you're not careful. But there's only one game of each. All Pokemon stuff works together, and the same with Bakugan stuff.

Be prepared, though. You'll hear more about these things than you ever cared to if your DS is into one or the other, and you may wind up cursing my name for suggesting it! It gets oooooold! crazy

Kriston