Data Card by SII

This is interesting although I did not read yet if it supports Windows Mobile devices. More details to be updated later.

Update: It seems like it supports Dell's Pocket PC 2003 so it probably supports WM 5.0 and 6.0, though not tested yet because I do not have a Pocket PC 2003 device with CF card.
http://www.sii.co.jp/mc/