Datel is now also offering a 4GB hard-drive with media player for the Nintendo DS.

Because the Nintendo DS lacks media player features Datel added them to a 4GB hard-drive. The Max Media Player for the Nintendo DS plugs into the game slot. After insert the media browser appears and you can play the stored MP3 audio files and videos and view JPEG photos.
Via USB you can upload media files onto the 4GB HDD to have them available on the Nintendo DS.
The 4GB Max Media Player for the Nintendo DS is available for pre-order on Lik-Sang for $179. It is supposed to ship in March. Visit Lik-Sang for more details on the Nintendo DS hard-drive.

Datel sells already a 4GB hard-drive for the Sony PSP.