I have done this project in the past with an accelerometer, worked really well. Problem being that accelerometer prices keep going up. I went to buy an accelerometer last weekend and found my chip of choice increased to over $20, yikes.
You may be chasing a "dinosaur". When chips go obsolete their prices tend to rise, this is a sign that something better/faster/cheaper has come out and there's really no reason to stick with that chip. For example, an MMA7660 accelerometer is only about $1. Would that work?
The Gadget Shield
: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons