ASPCA is fantastic! They give money to local animal organizations all over the country, not just New York (a common misperception). I'm a monthly ASPCA Guardian member. They draft any amount you like from your checking account. You get a newsletter with info on adoptions, where the money goes and such. Got the cutest 2008 calendar last week.
Petsmart also has a wonderful program. Just go to the Petsmart website for info. I've donated to them as well. Also donate to the Houston SPCA becasue of all the wonderful work they did when Hurricanes Katrina and Rita went through.
There's also your local rescue groups, Humane Society. Take your pick!
They help cats that are in bad situations. A large percentage of their cats have some type of chronic illness. I adopted my Malcolm from there 2 years ago. He is deaf and Diabetic and requires 2 shots of Insulin a day.
Find a charity that speaks to you. There are plenty to choose from.