A couple of sites that you can kill time at online and be contributing to good causes:

Play a trivia game to earn kibble for shelter animals at experienceproject.com and freekibble.com

Click to contribute to helping with hunger, breast cancer, child health, literacy, rainforest conservation, and animal rescue at thehungersite.com

Play a vocab game to donate rice to the UN World Food Program at freerice.com

Disclaimer: I can't guarantee that these sites do as they promise and donate to the causes they claim, but I like to believe they do (and snopes.com verifies both freerice.com and thehungersite.com). However, the games are a fun on their own, so why not? :o)