There's heaps of different uses for a barometric sensor, such as using it to forecast the weather or measuring altitude. The BMP180 sensor also includes a temperature sensor, and is accessible via an I2C interface.

Features:

 - 0.01hPa and 0.1 degree accuracy (altitude accuracy about 1m)

 - Libraries available to given direct altitude readout (search for BMP180)

 - Tiny module size