I just finished a video of my latest arduino sensor board. Many of arduino projects consisted of an UNO, display and various sensors connected through breadboards and wires. I wanted to reduce the clutter and have as many different sensors as possible along with a display that would fit in the palm of your hand. The first prototype was 1"x1" in size just to see how difficult it was to install an arduino bootloader onto a 328P. Once I figured this out it grew from there. The next revision will have a lipo charger behind the booster and a barometer. The MPL115A2 is a tiny i2c one that looks like it will fit. The code, gerber files and other details are at https://sites.google.com/site/0miker0/arduino-sensor-board
if you want to make your own.
atmega32u4 at 5V/16Mhz, TPS61200RDCR voltage booster, DS1340 RTC, ADXL345 accelerometer, TMP75 temperature, navigation and pushbutton switches, SPI and i2c breakout pins for connecting other devices.