This year I will walk at least 300 miles and bicycle at least 1000 miles for Charity Miles.
I think I've mentioned that app before. They line up corporate sponsors who donate to charities of your choice when you walk, run or bike. I usually support Habitat For Humanity or St. Jude Children's Research Hospital with my exercise.
A nice complementary app to Charity Miles is Donate a Photo. Every time you take a photo with your phone and "donate" it (you can do so once a day), Johnson & Johnson gives a buck to a charity of your choice (I usually choose Operation Smile).
When I say "charities of your choice," I mean that the above apps have pretty extensive lists of charities to choose from, not that you can type in any charity in the world. They have arrangements with enough worthy causes that you probably find something you consider worthy of your support.
Naturally, I'm planning to exercise more than just as resolved above. It's just a baseline. But a decent start, I think. Better to set a goal I know I can make with some, but not herculean, effort than to set a really hardcore goal I'm likely to give up on.