I got very excited when I saw the ESP8266 modules way back in September, a WIFI module for under $5, so I ordered a few ESP-01 and they arrived in due course.
The ESP-01 is great if you just want to add WIFI connectivity to your project, but once I realised you could program the onboard micro I knew I wanted access to the GPIO and other interfaces to make a standalone WIFI I/O node. I didn’t have to wait too long and back in November when I saw the ESP-03 module which breakouts a number of GPIO signals and interfaces to pads on the module. I ordered some and they arrived just before Christmas.
There are now over a dozen different styles (ESP-xx) of ESP8266 modules.
Here’s a few good ESP8266 links:
Espressif – the company that makes the ESP8266 SoC
Sites with good info. and tutorials