The Museum of Science and Industry has a fun online game to help students explore simple machines. The graphics on this game are expertly done!
The object of the game is to help the diminutive Twitch reach needed items, a task only accomplished through the use of simple machines. Players help Twitch navigate different levels as he discovers inclined planes, levers, pulleys, etc. They get to choose which of the simple machines he uses, and the site helps show students which simple machines require less work to perform a task. One of the goals is to preserve as much energy or effort as possible, so selecting different options allows students to evaluate which machines are better for specific goals.
This is a good resource to have to supplement your lesson on simple machines, or to use as a computer station activity for science.