As you may have heard we are at the start of a particularly virulent tornado season. (Around here I can count on one hand the number of tornado warnings and watches we usually get and we've had two already.) This latest batch that hit Alabama was looking to be a record breaker (and may succeed once the final counts are done.)
Smart Bitch Sarah has a lovely list of resources here.
You may well already have your favorite cheat sheet of charities, but, in addition to the suggestions on the link above, I'll add three more.
Shelterbox* provides emergency shelters in, well, a box. They are a UK based company but they provide shelters all over the world.
Feeding America, well, feeds America. (I swear I don't have a bias towards charities with their mission in their name, it just helps.) They work across the country networking food banks.
And then, Habitat for Humanity is there when it's time for people to rebuild.
*h/t to Maureen Johnson for the link.