Really? As in not just say you care about the situation in Darfour when you can't even point out where it is on a map? Yes, i am judging your first-world ass.
Go to these websites. They explain themselves.

"Man can live about forty days without food, about three days without water, about eight minutes without air, but only for one second without hope."

Give Water
What makes the desert beautiful is that somewhere it hides a well.
- Antoine de Saint-Exupéry

FreePoverty. Play darts with the World.
You get asked to pinpoint a city on the planet, and depending on your accuracy, anywhere between 0 and 10 cups of water are donated.

HelpThirst. Remember?
Designed to improve short-term memory by showing you a sequence of numbers and asking you to repeat them. Great if you think you have ADD. One cup per correct answer. It also helps improve your short-term memory.

Feed People
Rice is great when you're hungry and want 2000 of something.
- Mitch Hedberg

Hoongle. Google with a cause. <- No longer active.
It's just like regular Google, only it sends part of it's advertising revenue to the World Food Programme, enough to buy 20 grains of rice per search. Set it as your home page, or install the plugin to IE7 or Firefox.
I didn't find this one, Tancrisism did.

Free Rice. Feed people while you learn something.
Ansquer questions to feed people in need, one click = 10 grains of rice. Improve your knowledge of the following subjects in the process:
# Art;
# Chemistry;
# Geography;
# Languages (English, French, Spanish, German, Italian);
# Math.

There are people so hungry that God only appears to them in the form of bread.
- Mahatma Gandhi

Free Flour. Get enough flour to make buns or even loaves.
This one seems a bit newer than Free Rice and doesn't allow for choosing specific subjects. However, it's a lot more difficult than Free Rice, and a lot more ad intensive.
Thank you to seridon for posting this one.

Cure Diseases
We don't devote enough scientific research to finding a cure for jerks.
- Bill Watterson

Folding at Home. Be a part of the world's biggest supercomputer.
Connect to a central server that will use your PC's unused processing power to look for cures to a myriad of diseases:
# Alzheimer's disease;
# Mad Cow (Bovine spongiform encephalopathy);
# Creutzfeldt-Jakob disease;
# Lou Gehrig's disease (Amyotrophic lateral sclerosis);
# Huntington's disease;
# Parkinson's disease;
# many Cancers and cancer-related syndromes.
This last one is specially interesting if you're too lazy to click to feed dying children while reaping benefits for yourself (see above). You just install the client on your PC and pretty much don't need to do jack after that except go online from time to time. Great if you have the habit of leaving your PC on overnight.