Several years ago, I used to make and sell things (cards, paper crafts) on Ebay and use the ensuing Paypal money to donate to this cause or that political party. I'd have this secret donation bucket that was "mine" and I could use it to support my crazy fringe wacko causes. In fact, I was still using this model when I joined Company Shops Market in 2008. I told myself that I had to wait until I had the $100 in Paypal in order to join it. (In the end, I wrapped up a large box of too-big clothes and sold it and that put me over the top. And they turned out to not be so crazy, fringe, or wacko. Better luck next time! Ha ha.)
At the time, there was something so frivolously "extra" about donating to causes that I didn't want to use my "real" money to do it. My values were different then, and I viewed spending on clothes as mandatory but spending on causes as optional.
With events over the last few years being what they were, I have experienced a massive wake-up call in multiple areas of my life. (I'd highly recommend an awakening of this sort to everyone, though my hope is that you'd accomplish it in a more constructive, more painless way than I did. I'd recommend: finding religion, losing a bunch of weight, changing jobs, start running, etc. Something fun.) Anyway, my opinions about money have changed. A lot. More than it is possible to describe here.
Long story short, one of the goals of the Green V. Green experiment is to save money by simplifying and cutting back. This means, in part, being a conscious and skeptical consumer. And by conscious and skeptical I mean neurotically hyperaware of every single thing that I am buying and why. And one of the benefits from THAT is that I have a bit of extra money now to donate to my favorite causes, because I'm not buying as much stuff. For example, causes have been elevated in importance, and clothes spending has dropped way down in importance. (In fact, last month I spent $13 on clothes and that was at the thrift store.)
I've got a few pet causes: The Story of Stuff project, Sierra Club, Mountains to Sea Trail, ilovemountains.org (Appalachian Voices), Electronic Frontier Foundation, Doctors without Borders, Greenpeace, etc. A few more. I try to give to causes that (1) I really believe in and care about, (2) really need the money, and which are (3) accountable and trustworthy. Being a mindful consumer extends to donations too.
Check GuideStar, or Charity Navigator or Charity Watch to make sure the people you are giving the money to are on the up-and-up.
Note that only 501(c)3 organizations are on these sites. Groups like the Sierra Club or Greenpeace are 501(c)4 groups (more political) so contributions to them are not tax-deductible and they don't have to disclose their donor lists, etc. They are a different sort of charity. Groups like Appalachian Voices and the EFF are 501(c)3 groups so they are tax-deductible.
Find something that you really believe in, and which really needs you. Give some money.