Ever stumbled on a site that says, Click here to plant a tree, feed a hungry child or save a tiger? It's true, it's that easy! Of course it's only pennies-- or sometimes fractions of-- but it does add up. If you had a penny for every single person in the U.S., you'd be a millionaire three times over.
A very comprehensive site for donating by click is at The Non-Profits.com. ; the site lists more than fifty opportunities to give. Check it out.
A personal favorite of mine is Care2. I've been a member for some years, now, and the site just keeps getting better and better. Start here for Click to Donate. Better yet, if you want to see your efforts as they accumulate, create an account and the site will keep track of how many feet of rain forest you've saved, how many chimps you've fed, how many pounds of carbon you've offset, etc.
Don't stop with Click to Donate, though. Care2 has a great news service for people particularly interested in animals and the environment (although the site covers everything) a petition site, a great ecard collection, and more. Community is an overused word on thw web, but you really will find a great community at Care2.