Last month, in honor of the birthday of a couple of great kids, I made a donation to a food bank. Today I got a call from the President of that food bank thanking me - which I thought was very, very nice and greatly appreciated. It reinforces two things: 1, no donation is too small 2. every donation makes a difference. Special thanks to C & N for being so cool and inspiring it.
Something people don't do all to often is vet the charity. I know it seems silly, but there are many charities that are corrupt and many who have very high overhead and expenses such that only a fraction of each dollar you send actually gets used for the charitable cause - the rest go to inflated salaries and other unwarranted expenses.
There is a pretty good web site called Charity Navigator that rates many of the charities out there, at the very least, use that before sending your cash.