WiFi Module ESP8266 ESP-01 - 4MB Flash

ESP8266 is a highly integrated chip designed for the needs of a new connected world. It offers a complete and self-contained Wi-Fi networking solution, allowing it to either host the application or to offload all Wi-Fi networking functions from another application processor.

Examples are available at Seeed Wiki, Instructables and Forum.

More information is available on the website of Sparkfun.