Adafruit HUZZAH ESP8266 Breakout Board

Added Features
• Reset button
• User button that can also put the chip into bootloading mode
• Red LED you can blink
• Level shifting on the UART and reset pin
• 3.3V out, 500mA regulator (you'll want to assume the ESP8266 can draw up to 250mA so budget accordingly)
• Two diode-protected power inputs (one for a USB cable, another for a battery)
• Onboard 500mA 3.3V regulator, level shifting, and CE/FCC emitter certified. 

Two parallel, breadboard-friendly breakouts on either side give you access to:
• 1 x Analog input (1.8V max)
• 9 x GPIO (3.3V logic), which can also be used for I2C or SPI
• 2 x UART pins
• 2 x 3-12V power inputs, reset, enable, LDO-disable, 3.3V output

One breakout at the end has an "FTDI" pinout so you can plug in an FTDI cable (895-TTL-232R-3V3) or console cable to upload software and read/write debugging information via the UART. When you're done with your coding, remove the cable, and this little module can be embedded into your project box.
• Dimensions: 25x38x5mm/1x1.5x0.2"
• Weight: 5g
• The ESP8266 runs on 3.3V power and logic, and unless otherwise specified, GPIO pins are not 5V safe. The analog pin is also 1.8V max.

Power: The ESP8266 requires 3.3V power voltage and peaks at 500mA of current for small periods of time. You'll want to assume the ESP8266 can draw up to 250mA, so budget accordingly. To make it easier to power, a high-current-capable 3.3V voltage regulator is on the board and can take 3.4-16V and supply the current for the ESP8266. There are two inputs for the regulator, V+ and VBat. Both have Schottky diodes so you can connect both at different voltages and the regulator will simply power from the higher voltage. The V+ pin is also on the FTDI/serial header at the bottom edge. We recommend connecting your LiPoly or "AA" battery pack directly to VBat and then keeping V+unused for when an FTDI cable is attached There's also a 3.3V output from the regulator available on the 3V pin. 

Serial Pins:
• RX and TX are the serial control and bootloading pins and are how you will spend most of your time communicating with the ESP module.
• The TX pin is the output from the module and is 3.3V logic.
• The RX pin is the input into the module and is 5V compliant (there is a level shifter on this pin)
• The pins are available in two places, one set is on the right side breakout. The same pins are also at the bottom of the "FTDI/Serial" breakout.

GPIO Pins:
• This breakout has 9 GPIO on pins 0, 2, 4, 5, 12, 13, 14, 15, and 16; all GPIO are 3.3V logic level in and out and are not 5V compatible.
• These pins are general purpose and can be used for any sort of input or output. Most also have the ability to turn on an internal pullup. The only 'strange' pin is GPIO #0, which does not have an internal pullup, and is also connected to both a mini tactile switch and red LED. This pin is used by the ESP8266 to determine when to boot into the bootloader. For this reason, we don't recommend connecting anything to GPIO #0, because if the pin is held low during power-up it will start bootloading. That said, you can use it as an output and blink the red LED.