This pressure sensor from Freescale is a great low-cost sensing solution for precision measurement of barometric pressure and altitude. The MPL3115A2 has a typical 1.5 Pascal resolution, which can resolve altitude at 0.3 meters (compare to the BMP180 which can do 0.17m). It has some upsides compared to the BMP280, such as interrupt outputs for ultra-low power usage, and its also a heck of a lot easier to read altitude with a built in altimeter calculation – no calibration reading and calculating required. As a bonus, there’s even a fairly good temperature sensor with +-1C typical accuracy (+-3C max).
This board/chip uses I2C 7-bit address 0x60
Resources
MPL3115A2 Datasheet
EagleCAD PCB files on GitHub
Fritzing object in Adafruit Fritzing library