Cornell University
Cornell University: Astronomy: Aristarchus
This site from Cornell University provides a discussion of how Aristarchus arrived at his conclusions of the distance from the Earth to the Sun and Moon. Also has his methods for determining the size of the Moon and the Sun.
University Corporation for Atmospheric Research
Ucar: High Altitude Observatory: Aristarchus of Samos (310 230 Bc)
A brief biography and discussion of Aristarchus' theories provided here.