You can do this at freekibble.com, where you'll be presented with a daily trivia question. Whether your answer is wrong or right, shelter dogs will get 10 pieces of kibble. Rather feed cats? Go to the sister site, freekibblecat.com.
Both sites are simply and brightly designed, fun to look at, easy to use. There most interesting thing about them? Both are the brainchild of a young girl in Bend, Oregon, who wanted to help bring good food to the dogs at her local animal shelter. She had the idea and did most of the sponsor-finding and masterminding all by herself (her parents, professional web designers, did that part).
Go now to freekibble.com or freekibblecat.com!
A big thank you to Doug for sending me the clipping from the Oregonian about this site.