I am participating in Worldbuilders again this year. I bought a sheep.
I love Heifer International as a charity, because their work has a real impact on the real lives of real people. They let you choose exactly what you are donating and you know that your money will change someone's life with that goat or rabbits or seedlings or whatever you choose. There is a limited selection of specific items on the Worldbuilders donation page, but if you check out the Heifer International Gift Catalog, you can see the kinds of things they do. They have some pretty cool and clever packages. (The knitter's basket is not what you would expect).
I mean, medical research is nice and all, but who ever gets to say that their life was changed because one person donated 100$ to cure their cancer. 100$ doesn't go very far in a practical sense in the medical world, especially after the admin costs and fundraising costs that those big charities spend most of it on. Besides, everyone wants to get rid of cancer and lung disease, so they aren't hurting for donations. But not everyone cares about that one family in a poor country whose lives would be better if they just had a reliable source of food. I want to help them.
Oh yeah, and the cool thing about donating through Worldbuilders? The lottery. You get entered to win some awesome donated books and things. So you just might get a good read along with your warm fuzzies!