Evolution can be a tricky (but by absolutely no means impossible!) process to observe. This can make teaching students about the theory of evolution somewhat difficult compared to more readily demonstrable concepts such as magnetism or acid-base chemistry.

Computer simulations of evolution offer an excellent solution to this problem. Using these simulations, students and scientists can explore the process of evolution and get (in some cases highly visual) results in a matter of minutes. Luckily, thanks to intrepid biologist/programmers, many of these sexy in silico simulations of evolution are now freely available for download! Here are a few, at a glance:

Breve Creatures

Gene Pool

Java Evolution Simulator

Java Biomorph (Java implementation of the Dawkins Biomorph program)

Mushroom Life

(OK, its not a true evolution simulator, but I have a soft spot for Conway's Game of Life. And mushrooms.)

See also:

Dr. Saul's Evolution Lab
Evorunners
Flow in games
Maxis 1990 computer game Simlife
Discussion of the validity of computer simulation to provide evidence for evolution.