Just as Reggie explained a few days ago, the Wii console does indeed have a flap on the front panel. When lifted up, a SD card slot is revealed.
"That is where an SD card goes. That's storage media. And on top are the attachments for the GameCube controllers. It will be one of the memory mediums, and it's the only one that we've announced."
In recent weeks alot of sites have been speculating of other secret features hidden under this flap, but as you can see from the photo there is only a SD slot. However, there is a new button. Some think it says "SYNC" and would possibly be used to synchronize with the wireless controllers.
This actually sounds like quite a feasible idea as lots of existing wireless products have a button to do this. Obviously we'll have to wait for the final build Wii design to know for sure.