So there is a free application available for the iPhone, and 2nd generation iPod Touch. Its called Roller Coaster Physics. Its uses the built in accelerometer to measure gravitational forces. So just for kicks, I went to DL today and rode a few rides and recorded the ride to see what the results were. Below are the results the program gave, so I'm not sure how accurate they are, but here you go:
Space Mountain: 2.92 durring the drop
BTMRR: 3.37 durring the double helix after the second lift
Matter Horn (TL Side): 2.42 just after the first monster
Star Tours: 2.23 just after the Deathstar explodes
Here is a link that will open iTunes and take you to the app store:
Will definately have to try it on the rides over in California Adventure after I get back from Spain.