Since I am a dialysis patient and on a kidney transplant list, I would like to recommend the National Foundation for Transplants (transplants.org), Donate Life America (donatelife.net) or the National Kidney Foundation (kidney.org).
Not sure what types of fundraisers would work on a small campus, but these are definitely some wonderful organizations.
What a coincidence! I didn't notice which forum this was in when I posted, and I have to admit not being familiar with Phi Sigma Sigma - I looked at your national website and see that you are already involved with the Transplant Games, so I was suggesting something your organization is already familiar with!