Thermocouple amplifier is an outstanding analog-output amplifier that is easy to use.
MPL3115A2 - I2C is Barometric Pressure,Altitude and Temperature Sensor
BMP180 is a Barometric Pressure Sensor Breakout Board that can be easily interfaced with Arduino.
IR Thermometer Evaluation Board - MLX90614 is running on ATmega328 to evaluate the IR Thermometer
Barometric Pressure Sensor Breakout - MPL115A1 sense the barometric pressure by giving digital readings
Waterproof DS18B20 Digital temperature sensor + extras is a sensor that can give digital temperature readings in a waterproof device
Barometric Pressure Sensor - BMP180 Breakout is able to measure the Barometric pressure
Weather Shield provides you information about all the weather elements
Grove - Temperature & Humidity Sensor Pro is a sensor that can give accurate reading of both temperature and humidity
Weather Meters is apt for weather watchers who are keen to keep track.
Sparkfun Digital Temperature Sensor Breakout - TMP102 is a temperature sensor breakout with a digital output
Humidity Sensor - HIH-4030 Breakout makes humidity readings easier to determine and reduces the processing time.