Of course you can always donate money to the Red Cross and countless other organizations (please do), which you can find listed alongside many tornado outbreak news articles. But it's a little harder to find where to actually show up or who to call to register for hands-on help in Alabama, probably partially because thousands of volunteers showing up out of the blue might add to the problem. However, there are some smaller organizations advertising for volunteer help needed. I know other states were hit too, including the state where I live, but I believe it's a Cat-in-the-Hat situation in Alabama (...And this mess is so big and so deep and so tall, we cannot pick it up, there is no way at all). I think the ratio of hands to rubble is far worse than in Georgia.
New info added April 30th 2011!!