Seagate recently started offering their GoFlex Satellite line of hard drives that allow you to access your data wirelessly over wi-fi. On top of the wi-fi hard drive feature is the fact that the GoFlex Drives are battery powered as well. The battery should allow the Seagate GoFlex Hard Drive work for up to 25 hours.
The hard drive will allow wireless access to your data from an iPhone, Android, or tablet. Neat, but I must be missing the reason I "need" this drive.