Originally designed for a Palm V, this project interfaces a MMC (multimedia card) to any host via a 115kbps serial link. Access to the card is given at the sector level, leaving the implementation of a file system to the host. Based around the 2313, it illustrates use of software SPI, UART, and the sleep command. The whole thing runs of 2xAA batteries.
More information will be available shortly at http://homepage.ntlworld.com/seanellis/technology.htm, and host implementations will be hosted on Sourceforge under project "MMCSerial".