I need an Ethernet interface chip (10M will do) but instead of a normal
parallel memory mapped connection to a uC, I'd like to use either I2C or
SPI. Does anyone know of any devices that use a serial interface?
You might want to take a look at the Lantronix Xport device, ethernet on one
end, serial async port on the other. It will also allow you to download
custom applications, the entire TCP/IP stack is available through an API.