1.) Opera Browser: Wii remote is basically a mouse. If you have to type text, you can use a prediction thingy that works fairly well. Still if you have a computer, it's better for general browsing. Works best for YouTube type services, particuarly if your TV screen is bigger than your computer monitor.
Can also stream from iTunes, but I have yet to try this.
It's not exactly a system-deciding feature, but I guess it's nifty.
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Trauma Center: 2nd Opinion is a remake of a DS game and works very well. Even though it's a 1P game, you can kind of do 2-player with it ('Doctor' with the remote, 'Nurse' with the nunchuk selecting tools)