Disk System, a japanese exclusive add-on to the Nintendo Famicom known as the Disk System allowed the 8-bit console to load games from a re-writable source. Thanks to that interface, it was possible to come with a modern storage solution: FDSStick, a Famicom Disk System (FDS) drive emulator.
The FDSStick adapter comes with a USB port on one end, and a cartridge style connector on the other, so you can use USB devices as a replacement for the old disk units.
With a case, the device starts at USD40.
Source: Retro Collect
The FDSemu has just been released and offers double the storage, along with support for unofficial roms to name but a few improvements over the FDSStick.