Buy

http://www.seeedstudio.com/depot/grove-temperaturehumidity-sensor-pro-p-838.html

Wiki

http://www.seeedstudio.com/wiki/Grove_-_Temperature_and_Humidity_Sensor_Pro

C++ Library

https://github.com/Seeed-Studio/Grove_Temperature_And_Humidity_Sensor

Hardware

Arduino code

#include "DHT.h"

#define DHTPIN      A0
#define DHTTYPE   DHT22

DHT tempAndHumi(DHTPIN, DHTTYPE);

void loop(void) {

}

void setup(void)  {
  float humiVal = tempAndHumi.readHumidity();
  float tempVal = tempAndHumi.readTemperature();
}