This site by Holt McDougal provides a wealth of activities, simulations, and resources for Earth Science.
http://sunshine.chpc.utah.edu/javalabs/java12/machine/act1/lab.htm
http://www.teachengineering.com/index.php
http://www.grc.nasa.gov/WWW/K-12/Summer_Training/KaeAvenueES/pulleys.html
pulley activity w/o pulleys
http://edtech.kennesaw.edu/web/simmach.html
many simple machine links
http://tonto.eia.doe.gov/kids/
http://phet.colorado.edu/index.php
The links came out a bit wonky...just click on the blue http part and they should work!!