The balance board is a must. If you get the one that has the Wii Fit Plus game in it, it has lots of fun mini type games in it that the whole family can enjoy:
Martial arts to music, dodging soccer balls, snowball fights, down hill skiing, obstacle courses, just to name a few.
They sell chargers for the remotes, but I didn't invest in one. I just bought a bunch of AA batteries. So far so good (got ours last xmas). The batteries last a pretty good while. But I think the charger things don't require you to remove the batteries to recharge them, which would be a definite plus.
My 9 yr old daughter really likes the Just Dance Wii games. But then, she also loves Indiana Jones, Batman lego, and the Mario games too. She also really enjoys the Pilates/Yoga stuff on the WiiFit game. My son is more into Mario than our daughter is. He's 12.
I'm planning on getting our kids Epic Mickey for Xmas this year.