Choosing Charities

I have a hard time choosing which charities to give to. They all seem so worthy. How do I decide?
I usually give to the local NPR station. I love NPR. I would not have survived being a stay-at-home mom without the intellectual stimulation of NPR. It seems right to give to something that I'm using daily.
I also give to the local YMCA. My kids have done sports at the YMCA since they were little. Now only Tucker continues to swim there, but I know plenty of other kids who don't have the money or are in danger of becoming obese can go to the Y and learn how to play soccer or basketball. That seems worthy too.
With the slow economy, I also felt like I should give to the local food pantry. Making sure people have enough to eat seems more important than playing games or listening to NPR, right?
But wait a minute, I just got something from the Sierra Club explaining how the earth might not even be habitable unless we take some action. I mean, what good does it do to provide food and exercise for people along with intellectual stimulation if the earth becomes too warm or too watery for people to live here. We have to take care of the earth.
Then I get an email from a politician or a political party pledging to make things better in the economy, which could fix the hungry people, and they also promise to help clean up the oceans and wean the U.S. from its oil fixation so the earth can be healthy again. Maybe I need to support the politicians and trust them to improve our country and our planet.
It's so hard to prioritize.
Then I'll see a picture of little children in an orphanage and I'll be sucked right back to thinking that I need to donate to them instead. It's a vicious cycle for me.
Which charities do you donate to?