I have used Easy Off (heavy duty or something I believe) oven cleaner quite a few times with good luck. I just spray it on liberally and let it soak for a few hours then take it to the car wash. The combination of the cleaner and high pressure water will typically take almost all of the grease off if you spend enough time. It will also take off the factory paint on the frame and inner fenders, so keep that in mind if there are areas you do not want the paint to come off. Of all the methods I have tried, this seems to be the quickest and easiest.
