What about Guitar Hero: World Tour? If you're a Wii-only owner, it's a must-have.
I'm in the same position as you though... I might just buy the WiiSpeak peripheral for Christmas. I'll have it for The Conduit, at least.
Random game thought :
Why is Bionic Commando Rearmed 2 getting so much hate? We finally get a real game and they're not even satisfied... I'm starting to hate the gaming community so f****** much...