W5100 Ethernet Arduino UNO Shield

Ethernet Shield can be used to connect the Arduino board to the internet
Can be used as server or client.
This Arduino Ethernet Shield is based on the Wiznet W5100 Ethernet Chip.
Arduino Ethernet Library support
Onboard micro-SD card slot, which can be used to store files for serving over the network.
Compatible with the Arduino Duemilanove (168 or 328), Uno as well as Mega (1280/2560) and can be accessed using the SD library.
The Wiznet W5100 provides a network (IP) stack capable of both TCP and UDP.
It supports up to four simultaneous socket connections.
Use the Ethernet library to write sketches which connect to the internet using the shield.