It's good to see you're thinking of this. I'm a tax agent and so I see the receipts (or lack of) for people's donations. I get really disappointed when I see people on high salaries who make no donations, or go to the effort to keep their $2 donation receipt so ensure I claim it! I even had one guy the other day say he was going to donate to the bushfire victims but thought they had received enough money already so didn't. I thought this myself but still gave something and the rest to the poor animals instead. Even if you don't agree with a certain charity, there are plenty of others so there's no excuse not to donate something. I'm not saying I'm completely innocent, I could donate more than I do, but after I see how little others donate from my job, it just angers me a little.
In answer to your question j_p, I did World Vision for about 8+ years. She was a 5 year old girl from Swaziland, and it ended when World Vision considered her town set up enough that they could leave. I didn't go onto sponsor another child because I felt I had done my bit, and instead donate to various charities (I feel strongly about animal cruelty so help WWF, RSPCA, WSPA etc.) without the commitment. Once you start with a World Vision child, you won't be able to give it up (I don't mean they hold you to it, I mean you won't be able to bring yourself to). At least I couldn't. I started when I was a student, and even when times got tough, there was no way I could give it up. I felt a bond with my sponsor child, you write letters to each other and get photos and reports etc. and it's really touching. Definately worth it, knowing your little bit each month is changing a childs life. I remember when I initially signed up, World Vision tried to talk me into sponsoring a little boy because more people sponsor girls. I've seen too many documentaries on how those girls are treated in third world countries, so I chose a girl deliberately in the hope that the more that get educated, hopefully slowly they will be considered equal one day.