This year I decided to do something different - instead of donating money to several charities, I decided to donate to just one - water.org. Not only that, I've created an campaign, where I can keep track of what I've donated (and where others can donate as well).
Water.org does an incredible job of helping people getting clean water, often enabling children to go to school instead of spending all their time carrying water back to their home.
If you have some spare money, and want to support a good cause, I can certainly recommend this particular charity (which is secular).
Part of my concept is that what I donate should at least match what I spend on t-shirts and books, since I have too many of these things, and instead should try to help others. In all honesty, I am a bit behind on this, so expect my donations to go up a bit before the campaign finish.