[Al Skierkiewicz]

All of this is great discussion but here is something to think about...
From wire tables, #10 wire is 1.015 ohms/1000' or .001015 ohms per foot. Ohms Law suggests 100 amps through .001015 ohms=.1015 volts. With a little amplification this is a useful voltage. What's more, the impedance is very low and will generally not be susceptable to noise.
In looking at the op-amp circuit earlier in the post, I expect that the battery is used to supply a negative power supply to the op-amp. I would recommend a dual 9v battery bi-polar supply in that application to insure a zero volt output when there is zero current flowing.
As many of you who are working on current monitoring are aware, the current feeding a speed controller is pulsed, the same as the current being delivered to the motor. Therefore even after you sense and amplify, some other method of determining or scaling needs to be done in order to have a useable signal. We are currently working on a multi-channel current monitor circuit and will have details as soon as we get to a fully functional design.
Good Luck All