Discover magazine sponsored a contest where you had to produce a two minute video explaining evolution. The judge was PZ Myers. Here's how PZ explains his choice [see The Winner: Evolution in Two Minutes].
Oh dear. Repeat after me, PZ, evolution is not natural selection!
This is, indeed, the 21st century, and not the Victorian England of Charles Darwin. We now know that evolution is any change in the frequency of alleles in a population. We know that for evolution to occur the change has to be genetic. We know that populations evolve, not individuals. We know that there are two main mechanisms of evolution: natural selection, and random genetic drift. It's a good idea to mention that variation within a species (population) arises from spontaneous mutations that create gene variants called alleles. That's what needs to be explained in two minutes.
Here's the winning video from Scott Hatfield, a high school biology teacher, and, more importantly, a blogger at Monkey Trials. Scott's a cool guy but it's not the video I would have chosen.