Instructables

http://www.instructables.com/id/ICARUS-The-Analog-Heliosat/

Using clockwork: http://www.instructables.com/id/HELIOSTAT/

Using Arduino to calculate where you need to point: cerebralmeltdown.com

A complete history of Heliostats: http://www.redrok.com/main.htm#mechanical

Commercially available: http://lightmanufacturingsystems.com/order/