It's the
Nomad Jukebox you're talking about. The older Nomad was just a Creative Rio that took memory cards.
There are currently five different memory standards out there on the market for MP3 players...Thankfully, only two are really dominant:
Compact Flash - Currently the dominant type of memory. Cards currently offered have memory capacities of 480MB or more. IBM and others also develop miniature hard drives called "MicroDrive" which can use this interface in most newer players/digital cameras. This interface, called Compact Flash+ or CF+, also allows for use of generalized I/O devices.
Socket Communications has made serial/parallel I/O controllers and ethernet adapters which fit onto a CF+ card.
SmartMedia - Co-created by Toshiba, these things are really small and kind of fragile. Originally used in the Rio, they have a maximum capacity of 64MB, but cards those big are only readable in some devices, due to an original limitation in the implementation of SmartMedia.
MultiMediaCard - These cards are about 1" square and were used for a little while in digital cameras, such as the original HP PhotoSmart.
SD Card - Successor to MultiMediaCard, they look like wider SmartMedia cards. There are only a few players that currently support this. It's basically the lovechild of MultiMediaCard and the Recording Industry's SDMI.
Memory Sticks - Used only by Sony. More durable than SmartMedia, and thinner.