According to Wired Blog Network's GeekDad, if everything else fails, a good old fashioned smack on the back of your WiiMote might revive it.
GeekDad's WiiMote suddenly stopped responding to motion. After running out of options to fix it, the GeekDad decided to call Nintendo's tech support, and here is what happened in his own words:
"I explained [to Nintendo's tech support] what the problem was and what I had tried. She then asked me to check one more thing - the Wii Sensor - which checked out. Then the conversation went something like this:
Friendly Nintendo Help Desk Lady: "Okay - I want you to take the remote, button side down and smack it into the palm of your hand two or three times."
Russ: "You've got to be kidding"
Friendly Nintendo Help Desk Lady: "No sir, do it hard enough that I can hear it across the phone line but not hard enough to damage the remote"
Russ: "You're sure?"
Friendly Nintendo Help Desk Lady: "Yes, sir."
So, button-side down, the funky Wii remote got smacked in the palm of my hand three times....
...and the thing worked!
Now, why don't they publish this fix on the support site?"