Freekibble.com and freekibblekat.com work like this-
They have a trivia question about dogs or cats, you click the answer, and whether you get it right or wrong, they donate ten pieces of kibble to dogs/cats at shelters. Freerice.com is the same, every question you answer you donate ten grains of rice to the poor. And both are totally free and you dont have to have to have an account or anything! I do these whenever i can cause i think its awesome. :D