For those who don't understand that any SD card will work in your Wii, the 2GB Rock Band 2 Secure Digital card will reportedly hold up to 75 downloadable songs -- or 2GB of anything, actually.
The non-Ben Heck aspects of the device seem to be decent enough as well, with it boasting a 480 x 234 LCD display (the exact size isn't clear), an SD slot to handle all storage needs, and even a port to connect two systems together for multiplayer games.