The Vegetarian Journal is one resource that you can either subscribe to or locate online. As a journal, it publishes scholarly articles that intend to show the benefits of a meat-free lifestyle via advocating what they refer to as "cruelty-free" dietary choices.
Here on Enotes the Gale Group offers articles on veganism from the Encyclopedia of Nursing and Allied Health for which there is a link included at the end of this answer.
The People for the Ethical Treatment of Animals (PETA) is perhaps your best choice. Their website offers background information on dietary choices and why they should be made. Moreover, PETA is linked with a number of universities, celebrities, and researchers who actively engage in encouraging people to choose meat-free lifestyles.
Lastly, keep your eye open for articles by Colin Spencer, who has written extensively on the vegetarian lifestyle and veganism as a choice for a healthier life.