Mitosis, that process of cell division that results in new cells, is taught in second-year biology. (It still is, right?) The whole process goes through various phases, which textbooks often illustrate.
Wouldn't it be great if it were animated, though?
Cellsalive.com has it -- animal cell mitosis, the animated version. Clicking on a "phase" shows you a still image of that phase, so you can move back and forth to see the differences.
Some lessons really do need something more than textbook illustrations to be effective. With a process like mitosis, for example, it's better to see just how one phase flows into another. You could imagine it, but not everyone has that vivid an imagination.