I think the OP wants to divide one voltage by another voltage. That's what Laplace has assumed as well. He has given a good answer.
I think Laplace's circuit looks very interesting, but it has a 555 with a high impedance, first order filtered PWM signal as an output!
Ripple, high source impedance and slow response might be issues. Buffering and additional filtering might be needed (there are already 4 RC-filters in that circuit!).
The idea with a digital potentiometer would allow for a much faster and cleaner signal, with respect to the straight OP input voltage (dividend). Added of course the flexibility of the uC.
The divisor voltage would have to be collected on an A/D or comparator pin of a micro controller (or right away produced in software). Then translated into the right bit-length and format. Then serially output on 2 or 3 other uC pins to set the digipot.
Of course the divisor would also be subject to slow response time and digital quantification, but I suppose that would seldom matter.
As an example where I would use such circuit would be in an analog measure instrument, with accurate scaling of the input range (dividing the input signal entering the instrument).
In fact the simplest division circuit I can think of (without operational amplifiers) would be the
digital potentiometer itself. Setting the ratio of a potentiometer would divide the voltage over it in the way the programmer wishes (you could program any mathematical function).
The second solution I mentioned, with the JFET, is a very simple pure analog solution. Here I found the simplest possible division OP-circuit from an old National Semiconductor Application Note:
A more accurate, modern but still simple solution would be this multiplier circuit. It uses MOSFETs instead of JFETs:
Vout=(R2/R1)*v1*v2/Vref
Using Vref as input (and v2 fixed) would give the desired division function. Connecting v1 and v2 together, would give a squaring circuit on top of it.
For deeper explanation and also an example of Steve's log approach (as multiplier), see the Wikibook site itself:
http://en.wikibooks.org/wiki/Electronics/Analog_multipliers