Doesn't the Wii have an SD slot? Also speculations that the Wii will accept more flash memory mediums.
I believe SD flash cards go up to about the 4-8G range now and not too expensive too.
Then again, an external 80G 7200 RPM 2.5" hard drive via USB or eSATA (blazin' fast, might be possible?) would be nice for storage of photos, music, videos, etc.