Farm Sanctuary was founded in 1986 to combat the abuses of factory farming and to encourage a new awareness and understanding about "farm animals."
http://farmsanctuary.org/

The Humane Society of the United States is the nation's largest and most effective animal protection organization—backed by 11 million Americans, or one in every 28.
http://www.humanesociety.org/

The ASPCA works to rescue animals from abuse, pass humane laws and share resources with shelters nationwide. Their mission, as stated by their founder, Henry Bergh, in 1866, is “to provide effective means for the prevention of cruelty to animals throughout the United States.”
http://www.aspca.org/