The hypothesis that the combination of lead and copper in a Galvanic cell will have the highest voltage is proven to be true.
Galvanic cells are used by us everyday in the form of batteries. The batteries are actually made of many such cells. Their applications include the simple batteries used in portable devices such as the torch light and also the batteries that are used in cars. Batteries are also used to store the electrical energy generated by solar panels and wind turbines. Similarly the electric car also depends on batteries to supply the energy required for them to operate.
This science fair project can also be done using electrodes of different dimensions.
Try using different types of metal electrodes and solutions.
Try repeating the experiment at different room temperatures and compare the measured voltages.
Galvanic cell - http://en.wikipedia.org/wiki/Galvanic_cell
What is the galvanic cell? - http://www.wisegeek.com/what-is-the-galvanic-cell.htm
Always handle chemicals with care. Safety gear (goggles, lab coats and gloves) should be worn when handling chemicals.