Rechargeable AA batteries, they deplete after a week or two, even you don't play the Wii... It kinda suck balls, but i always have spares, so it's not an issue. Why can't the Wii just charge the Wiimote? If you add up the little things you buy for the Wii, there's a big chunck of change. I happen to have rechargeable batteries, so that's a "free" given. I'm way too cheap to buy the protective skins, i don't the point of them at all (except maybe different color to distinguish #1 or #2).
Here's my advice, use rechargeable AA and have some spares on the side... For parties, have some real batteries on the side (when they are on sale, you can get a good brand for pretty good price).
Why bother with this $30 piece of thing? I won't call it junk, but to me it is... I don't like plug things in the outlet most of the times, b/c it adds more on the electric bill.
This one thing i find the PS3 is well designed, you can charge the controllers via USB. What does that mean? If you're on the computer doing stuffs, you can charge the controllers. Heck, you can even charge the controller when you're playing the PS3. That's what i do, i got two controllers and one is plug in charging while the other is in use. I never got battery problems with the Sixaxis. On the other hand, the Wii, i almost always use my spare rechargeable AAs.