I wouldn't give to any national charity - most of them are top heavy and suck a lot of the money off for administrative fees. There are plenty of local bodies doing wonderful things. Astride, as Rug mentioned, is one. Another is the ARISE program, which provides assistance for kids with disabilities free of charge so they can participate in after school activities like sports, Scouting, church groups, theatre groups, etc.
Rant over. Good question!
Heather