Well, according to snopes.com and craig's list there are a few that are worthy and are not hoaxes.These clicks are no cost to you.
CharityUSA.com gives a percentage and in some cases 100% of the total ad revenue collected towards animal shelters and other organizations : The Rainforest, Breast Cancer and a Child Health Site.
See below the email I received. If you always wanted to get involved in a cause, but didn't know how to start, think about clicking...a little adds up and these are worthy causes. If you want to make sure this is on the up and up, check the below url's.
Help Feed the Animals for Free
Hi, all you animal lovers. This seems pretty simple. Please tell ten friends to tell ten today! The Animal Rescue Site is having trouble getting enough people to click on it daily to meet their quota of getting free food donated every day to abused and neglected animals.It takes less than a minute to go to their site and click on "feed an animal in need" for free. This doesn't cost you a thing. Their corporate sponsors/advertisers use the number of daily visits to donate food to abandoned/neglected animals in exchange for advertising. Here's the web site! There is also a few links to fight Cancer, feed people and the rainforest site. Pass it along to people you know.