University of Georgia
University of Georgia: Greatest Common Factor
This is geared to teachers with the objective of helping students use their TI-34 calculators to find the greatest common factor. Includes working examples.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Formula for Greatest Common Divisor.
This site is a question and response to a student asking Dr. Math about the greatest common divisor, he gives an interesting way to find the gcd, as well as the button on calculators which commonly does the math for you.