The ESP8266 is an exciting new WIFI device. It's suddenly become so popular because of an influx of cheap (£3) modules been made available on EBAY.
So obviously you have been able to get USB WIFI devices for this price for a while but now they even have all the processing and even some GPIO on board so all you require to access them is a serial port and a few AT commands. This makes WIFI practical for any Arduino/PIC/uC application that has at least one serial port which is a very low bar indeed!
Any way Just seen a YouTube vid of some guys doing some impressive tests of the range of this device which in free line of site was over 400M!!
Take a Look: