You mentioned contacting pet organizations. A good one to look at is www.animalrescuesite.org. Each click donates food and other care to animals which is sponsored by the advertisers on the site.

If you go to the site, you'll see a "link to us" link on the left. On that page they have several images you can use to link to them from your site. Text links are welcomed, too.

Nancy
http://www.CreateYourMarket.com
Marketing Ideas for the Home-Based Entrepreneur