People for the Ethical Treatment of Animals (PETA) offers the most comprehensive resource on how animals are exploited for food. Here you can find detailed, regularly updated factsheets on chickens, cows, pigs, fish, turkeys, ducks and geese. You can also find links to free veg starter kits, videos, photo galleries, and action alerts.
The Humane Society of the United States (HSUS), in the Animals section of their website under the heading of Farm Animals, you can find links to factsheets about the animals used and abused in factory farming as well as legislative updates on measures to improve their living and dying conditions and current HSUS action alerts.
Mercy for Animals has a great short video explaining what is wrong with factory farming and what we can do to stop this cruel industry. Here you can also find succinct descriptions on the torments animals endure on factory farms and links to undercover investigations.
Vegan Outreach has an informative short video explaining speciesism followed by general information on how animals are treated on factory farms and other ill effects of factory farming as well as a link to the Go Vegan section of their website for tips and tricks on going and staying vegan.