I've told people about this before, but new people have turned up since then, and anyway it never hurts to remind people.
There's a site here with a row of five tabs at the top of the page. One for Hunger, one for Breast Cancer, one for Child Health, one for Rainforest, and one for Animal Rescue. Click on the tab, find the Click Here button, and click. Make a bookmark and do it once a day, every day. Simple as that. You don't even need to read the rest of the pages to find out why what you've done is important (though it'd be good if you did).
It won't kill you to do it. But it may save a life or two.
Even better, tell your friends about it. Just copy this post and stick it in your journal. It only takes a minute.