The latest revision of the shield adds a micro-SD card slot, which can be used to store files for serving over the network. It is compatible with the Arduino Duemilanove and Mega (using the Ethernet library coming in Arduino 0019). An SD card library is not yet included in the standard Arduino distribution, but the sdfatlib by Bill Greiman works well. See this tutorial from Adafruit Industries for instructions (thanks Limor!).
The latest revision of the shield also includes a reset controller, to ensure that the W5100 Ethernet module is properly reset on power-up. Previous revisions of the shield were not compatible with the Mega and need to be manually reset after power-up. The original revision of the shield contained a full-size SD card slot; this is not supported.
Arduino communicates with both the W5100 and SD card using the SPI bus (through the ICSP header). This is on digital pins 11, 12, and 13 on the Duemilanove and pins 50, 51, and 52 on the Mega. On both boards, pin 10 is used to select the W5100 and pin 4 for the SD card. These pins cannot be used for general i/o. On the Mega, the hardware SS pin, 53, is not used to select either the W5100 or the SD card, but it must be kept as an output or the SPI interface won't work.
Note that because the W5100 and SD card share the SPI bus, only one can be active at a time. If you are using both peripherals in your program, this should be taken care of by the corresponding libraries. If you're not using one of the peripherals in your program, however, you'll need to explicitly deselect it. To do this with the SD card, set pin 4 as an output and write a high to it. For the W5100, set digital pin 10 as a high output.
The shield provides a standard RJ45 ethernet jack.
The reset button on the shield resets both the W5100 and the Arduino board.
This is the PoE Version of the Arduino Ethernet Sheild
The Ag9120-S is a module designed to extract power from a conventional twisted pair Category 5 Ethernet cable, conforming to the IEEE 802.3af Power-over-Ethernet (PoE) standard.
The Ag9120-S provides the PoE compatibility signature and power classification required by the Power Sourcing Equipment (PSE) before applying up to 15W power to the port. The high efficiency DC/DC converter operates over a wide input voltage range (36V to 48V typ) and provides a regulated low ripple and low noise output. The DC/DC converter also has built-in overload and short-circuit output protection.
Features: IEEE802.3af compliant Small SIL package size - 56mm (h) x 14mm (h) Low output ripple and noise Input voltage range 36V to 57V Overload and short-circuit protection High efficiency DC/DC converter (75% typ) 1500V isolation (input to output)
This module could be used with products Arduino Ethernet shield and Arduino Ethernet