ok, the problem lies in your speed sensor. It's shaft with a gear on it that's bolted to your tranny. take it out, take it apart, clean everything with carb cleaner (including the inside and outside of the plug and the wire it plugs into), let all the stuff evaporate, put it back together, start your car, turn your car off, reset your ecu (leave your negative terminal off your battery for 1 minute). If that doesn't fix the problem, buy a new speed sensor. If you really need a new one, send me a picture of your current one, I think that I might have one I can sell you.
My speedometer has been working on and off for about a month. It'll work for a few minutes somedays, other days it will work until it is triggered by a gear change. This was all fine and I didnt have any real trouble. I figured it was just the sensor. However, today my odometer (and trip meter) stopped working as well right after i filled up on gas. I tried pushing the reset button a bunch of times and it worked for for a few miles, and then the odometer stopped working again. Then the speedometer (which had been working during the first part of the day) stopped working. As I drove along the road, being pissed off at my car, the speedometer started working again and when it did, the odometer did too. WTF!!! 
Until this happenned, I assumed they two things were different, unrelated rpoblems, but it now appears they are in fact related. Is there some loose wiring or somthing that is causing the touchy malfunctioning of my odometer and speedometer? Please help!