Definitely check out PETA at
www.peta.org - especially look at their vegetarian websites ((broken link removed) (broken link removed) (broken link removed)
GoVeg.com JesusVeg.com KFCCruelty.com (broken link removed)
MeetYourMeat.com (broken link removed) (broken link removed) (broken link removed) . You can even get a free vegetarian starter kit, which may help you with your essay.
Also FARM (Farm Animals Reform Movement) is a great organization.
www.farmusa.org
In Defense of Animals is another good site -
www.idausa.org
www.upc-online.org (United Poultry Concerns)
www.hfa.org (Humane Farming Assocation)
(broken link removed) (Farm Sanctuary)
www.earthsave.org (EarthSave International)
(international vegetarian union)
www.mercyforanimals.org (Mercy For Animals)
www.navs-online.org (North American Vegetarian Society)
www.pcrm.org (Physicians Committee for Responsible Medicine)
www.vegetarianusa.com/ (VegetarianUSA)
You might also want to try some books .... 2 that are good are "A Diet for a New America" by John Robbins and "Animal Liberation" by Peter Singer.
Let me know if these aren't enough or what you're looking for. I know of more.