When I got my Wii, I was very surprised at the extra Channel (though not all are active yet).
I hope that Nintendo will continue to develop new channels. Channels that I hope to see in the future:
-Wii-Chat: already rumours about this, why create Mii-avatars and not be able to show them off proper?
-Wii-kipedia: Basically u can access this encyclopedia already on the brower, but it would be great to have a cutomized interface for the Wii.
-Wii-Music/Video: Playing MP3's is already available, but they could make it more easy. Now you need to put MP3's on a disc, create a slideshow of 1 picture in Picture Channel and set up random MP3 music from the SD in the 'A'-button menu during the slideshow. (credit to below posters)
-Wii-Tube: (we tube), makes use of a webcam connected to record and share vids with other players. Also have a live-option, to directly share video with friends. (why we need phones anymores?)
-Wii-Earth: Somewhat similar to Google Earth, internet maps of the world with roadmapping.
-Demo Channel: A channel where all Nintendo games can be reviewed. Players can write their own reviews here and post them on the games. Give ratings AND play the demo of the game.
-Virtual Console Channel: To organize all your VC-games properly.
-Wii-Screensaver: Fishtanks, Fireplaces, Tranquil landscapes with wind blowing through flowers and butterflies flying. Just any nice motion picture/ 3D rendering to put on the TV when you are having a party.
Maybe I am trying to turn my imaginary Wii into some sort of PC, but in fact the Wii is somewhat similar, but far more family-friendly then any Microsoft XP Multimedia PC can be.
Any more channels that you would like to see? Feel free to add them.
(secretly hoping Nintendo devolopers look at this thread for new ideas)