My immediate thought was to use a pair of resistors in a potential divider circuit, but I'm not sure that there isn't a better method of doing this.
if you do not need extreme speed, resistors work well. The only problem with a resistive divider is the time lag caused by the RC created by the resistor and stray capacitances. If the impedance of the voltage you measure is low, no problem, but of you have to make the resistors im the MegOhm range, you will need to consider this.

Erik