Compatible SD cards -- the kind you find in digital cameras -- can be used to store extra games, channels or save data. These cards should have less than 2 GB capacity and a relatively fast transfer speed. Additionally, Nintendo has licensed SanDisk and Bensussen Deutsch and Associates memory cards to work specifically with the console. The card slot is located on the front of the Wii. Just unhinge the plastic cover underneath the CD slot to access it.
To transfer files, select "Data Management" from the "Wii Options" menu. You can then select "Games" or "Channels," and then chose individual items to copy onto your SD card.
Unfortunately, you cannot access Wii channels or save games directly from the SD card, so it can only be used as storage. When you want to use a channel or load a save game, you must move it back to the Wii's internal memory.