Indiana Campus Compact is aggregating ways in which you can lend assistance to relief efforts.Splashlife's "Rebuilding from Devastation Campaign for Tornado Relief"
Latest updates for Joplin tornado recovery http://cot.ag/mqGZbi
From the Alabama Poverty Project
National VOAD (Voluntary Organizations Active in Disaster) is a coalition of organizations that respond to disasters.
National Relief Network (www.nrn.org>) matches groups with disaster projects. In addition to securing work for your group, they arrange housing and meals (which can be very difficult to do if you do not have any relationships in the impacted area)
YSA (Youth Service America) has a brief Service-Learning Tip Sheet specifically addressing Disaster Preparedness.
The American Red Cross: