Factoring the Greatest Common Factor from Polynomials:

Here is a link to a good description of the ac-method of factoring.

Factoring by Grouping, Factoring GCF first:

Factoring by Grouping, Factoring a GCF first (another example):

Khan Academy on GCF:

Factoring GCF

Khan Academy on factoring:

Factoring Quadratics