We touched on this when with the Rolls Royce programme thread. (Yes it turned to charity)
To reiterate my thoughts again, i donate to Air Ambulance, and Cancer Research, as well as the occasional good cause that maybe a friend does to raise money. I refuse to donate to firms like Oxfam, but them in particular. They have a nice swanky office tower next to the law firm owned by Tim Henmans dad, my mother in law works there, just outside central Oxford. You will find alot of large charities make stupid amounts of money. I stick to the ones that mean something to me, and I feel is a worth while cause, I also help my sister out with things if needed, as she is always on the borderline. I dont donate 10% of my salary to charity, but I feel I do enough.