That you can help the earth by clicking a button on a website.
Actually, several. ;D
They're click-to-donate sites, and they're completely free. (some of them you can register for, though, still free) The sponsors, who place their ads on the sites, pay for the donations depending on how many people view and/or click their ads. Clicking the ads isn't necessary, but if you want to, go ahead; it still helps ^^ Most sites allow you to click just once a day, so don't forget to bookmark them!
There's www.ecologyfund.com , the first click-to-donate site I ever found, which was about 7 years ago. I've been clicking there ever since, and since I registered there so it could track my totals, I've saved over 5 acres of land, in the rainforest and other endangered habitats. One of the organizations that benefit from this is The Nature Conservancy.
Owned by the same company, www.therainforestsite.com allows you to save 11.4 square feet of land per daily click. They also run an online store that's chock full of neat stuff, and your purchases there help save rainforest land, too. The Nature Conservancy, The Rainforest Conservation Fund, Rainforest2Reef (formerly Friends of Calakul), and other environmental charities benefit from this site.
Care2 is an amazing site all on its own. It has lots to offer there, but their click-to-donate area is very much worth mentioning:
http://rainforest.care2.com/ (this benefits The Nature Conservancy)
http://globalwarming.care2.com/ (this helps purchase carbon offsets)
http://oceans.care2.com/ (Oceana benefits from this one)
http://bigcats.care2.com/ (Wildlife Conservancy Society benefits here)
http://primates.care2.com/ (The Jane Goodall Foundation is helped by this)
There are also clicks there for baby seals (which funds efforts to stop the Canadian commercial seal hunt), kids (a set of children in other countries are sponsored through it), pets (which benefits The Humane Society of the United States), and more.
www.redjellyfish.com has two click-to-donate programs, one for rainforests, and the other for primates (also benefiting The Jane Goodall Foundation). You have to register, I think, but I think it's worth it.
www.landcareniagara.com says that for every 5 clicks, they'll plant a tree. I hope that's still true, 'cause that'd be cool! :D
You can find those and even more here: http://www.conservebirdhabitat.com/donation.htm
What I do now is just go to that website everyday, so I don't have to memorize or look up a bunch of links. Keeps things simple =)
It's a small thing, and there's a chance it may not be helping as much as I'd like it to, but I think it's still a good thing to do, and something that EVERYONE with a computer and internet connection can do. Heck, I have dial-up, and while it can be slow going sometimes, I still get it all done within about 15-30 minutes. Somebody with high-speed internet can probably do them in half that, or even less.
Oh, and don't forget about the non-environmental clicks as well =) If you go to The Rainforest Site, you'll see The Hunger Site, The Child Health Site, The Breast Cancer Site, The Literacy Site, and finally, The Animal Rescue Site.
and www.freerice.com , at which you answer vocabulary questions to donate rice to hungry people. Admittedly, I don't do this one often, but when you're bored, it's a great way to pass the time! :D (and learn something, too :P)
Another act of green some might find surprising? Reducing or eliminating meat in your diet.
Seriously, meat production contributes quite a bit to global warming, pollution, and habitat destruction. A report from the U.N. stated that meat production worldwide produces 18% of the world's greenhouse gas emissions, from the fossil fuels involved to the management, production, and transport, to the cattle themselves.
Large-scale factory farming produces quite a bit of pollution, especially water pollution. Grazing cattle need land, and this means other habitats have to be destroyed to provide it. Chickens and turkeys don't have as large of an impact on the environment, but the fact remains that it's better environmentally to eat a plant-and-locally-grown-foods-based diet.