There are sites out there, that much like the "insert a dime and you'll save an acre of rainforest" bubblegum machines you sometimes come across in museums, zoos, and aquariums, you can do something so tiny, you'll have a hard time believing you're doing something good for the world. I used to be a dedicated, die-hard clicker, with several sites bookmarked that I'd kick myself if I forgot to visit and do my daily clicks by midnight every night. Each time you click on these websites, some environmental, animal rights, civil rights, or otherwise similar extremely worthy cause feels the benefit, through ad revenue or donations or promised contributions.

Care2 is one of the best sites for supporting such causes. Aside from having 10 separate causes to click for, they have news, social networking, a daily action section, and a petitionsite, where you can put your digital signature on virtually any petition imaginable to support any cause which might interest you out there.
There are other websites out there like this, unfortunately they were bookmarked on my old laptop. So in the future, expect more helpful suggestions like this one, and for now, swing by and do your part every time you go online to check your email. It could NOT be any easier to make a difference in the world, no matter how busy you are.