This precision sensor from Bosch is the best low-cost, precision sensing solution for measuring barometric pressure with +-1 hPa absolute accuraccy, and temperature with +-1.0C accuracy. Because pressure changes with altitude, and the pressure measurements are so good, you can also use it as an altimeter with +-1 meter accuracy.
The BMP280 is the next-generation of sensors from Bosch, and is the upgrade to the BMP085/BMP180/BMP183 – with a low altitude noise of 0.25m and the same fast conversion time. It has the same specifications, but can use either I2C orSPI. For simple easy wiring, go with I2C. If you want to connect a bunch of sensors without worrying about I2C address collisions, go with SPI.
Key Features:

BMP280 sensor, an environmental sensor with temperature, barometric pressure that is the next generation upgrade to the BMP085/BMP180/BMP183
Used in both I2C and SPI
Measures barometric pressure with 1 hPa absolute accuracy, and temperature with 1.0 degree C accuracy
A low altitude noise of 0.25m and the same fast conversion time
Can use it with a 3V or 5V logic microcontroller
Product Dimensions: 19.2mm x 17.9mm x 2.9mm / 0.8″ x 0.7″ x 0.1″
Product Weight: 1.3g / 0.0oz

Resources
Datasheets, PCB CAD files, Fritzing object and more available in the product tutorial