Considering the state of the U.S. economy, we shouldn't be sending ANY cash. I understand providing humanitarian assistance in the form of personnel from government agencies, and possibly food and other supplies. If private citizens wish to donate, that would be their option.
Being the the U.S. is broke, at war and in serious financial trouble, shipping millions of dollars overseas to a sovereign foreign nation isn't a very responsible thing to be doing at this point in time.
I feel for the folks in Haiti, but we need to take care of the American people before we're able to assist others.