What's the source of electrical energy in galvanic cells? Let's take a simple Daniell cell for example: 

Where does the energy required to drive electrons through the external circuit and power up devices (like a light bulb) come from? Does the oxidation of zinc release that energy? And, does the reduction of copper result in more energy being released? (since we're calculating the cell potential by adding up the oxidation and reduction potentials of the two half cells). I've always wondered about this question, and I'd really appreciate a clear and concise explanation regarding this particular topic.
Judging by your above comment to beginner's answer, you seem to be confused about how reactions proceed in general.

Take a look at this graph : http://en.wikipedia.org/wiki/Activation_energy#/media/File:Activation_energy.svg

The oxidation in the beginning certainly requires energy, but at the end of the reaction, the system ends up at a lower energy state overall. This causes the reaction to be "spontaneous".