The ESP8266 Witty Cloud ESP-12F WiFi Module is a powerful WiFi enabled processor in a compact package that incorporates an RGB LED, LDR light sensor and pushbutton for easy stand-alone operation.

Witty Cloud board is one of the cheapest ESP8266 device you can get on the market. It has a microUSB port with USB-Serial interface, which means no soldering! The board also contains an RGB LED and a button, which allows me to use it without a breadboard.
Besides adding WiFi capability, the main claim to fame for the ESP8266 processor over the AVR processor of the standard Arduino is that it has a larger 4 MB of Flash memory and runs at clock speeds of 80 MHz and can sometimes optionally be overclocked to 160 MHz and therefore has a fast processing speed.