WiFi Shield

Connect your Arduino to the Internet anywhere you can find an access point with the official WiFi Shield! Each WiFi shield’s MAC address is registered with NCSU’s Nomad system, so you should be able to connect to the network ‘ncsu’ out of the box. Note that the network requires no security key.
 
For great documentation, see http://arduino.cc/en/Main/ArduinoWiFiShield. There are also several example WiFi sketches in the Arduino IDE software.