Nintendo...

Wii - The Wii needs tons of accessories and tons of add-ons to make it a great system. The accessories are fairly cheap and are good quality. Some of the accessories, you might want to stock up on them.

Original DS - The original DS doesn't need a lot of accessories, and they're fairly cheap. So, I think you know what to do! Stock up on them (when necessary).

DS Lite - Same accessories as Original DS (most). Similar accessories to the PSP, makes the accessories pretty cheap.