The LIS302DL is a triple axis I2C accelerometer that you can buy on a breakout board produced by Sparkfun pretty cheaply and is ±2g/±8g selectable. Its is easy to hook it up to an Arduino (SCL - analog pin 5, MOSI - analog pin 4, tie MSIO to VCC for I2C address 29 or gnd for 28).
There are a few handy examples to get started quickly, such as this and this. I had better readings when I turned in the internal filter.
