There are quite a few. The ones you start off with are as follows:
-Disc Channel
-Mii Channel
-Photo Channel
-Wii Shop Channel
-Weather Channel (or Forecast Channel)
-News Channel
-Message Board
You can also download more channels for free, and they are as follows:
-internet Channel
-Everybody Votes Channel
-Contest Channel (or Check Mii Out Channel)
-Nintendo Channel
-Today And Tomorrow Channel
-Netflix Channel
-Kirby TV Channel
Also, if you're willing to pay a price, you can download virtual console or wiiware games, for 500 wii points to 2000 wii points.
Finally, there are some wii channels you can only get by hacking. These are:
-Homebrew Channel
-MAG Loader Channel
-SNES Channel
-Snes9X Channel
-NES Channel
-FCEU Channel
-RIN Channel
-Genesis Plus Channel
-HUGO Channel
-ScummVM Channel
-WAD-Installer Channel
-WAD-Uninstaller Channel
-Wiimc Channel
-Riivolution Channel
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New channels can be downloaded from the Wii shop. Though most channels are free there are some that require you to buy Nintendo points to obtain.
The wii games don't give you channels. You have to go to the wii store, which you have to be able to connect to the internet, to buy the channels. Most of them are pretty cheap.
From your Wii options menu, select Data Management and then Wii Channels. Select the channel you want to delete and select "delete."
You go to the settings, then Data Management, then Wii Memory, then Channels, then click on a channel, the press 'Delete' or 'Erase'.
Too many to list, 100+