I'm applying to business school and they are looking to attract people
who want to make a difference.  While I haven't had much time to
contribute to charitable causes, I have made considerable donations to
a variety of organizations.  Is there an appropriate way to
communicate this on my resume?

"Donations" are an easy way out of trying to "make a difference" 

A real business school would rather you organize a fund raiser for
Senior Citizens or organize an info session for STDs etc

Maybe you could describe yourself as "a supporter of the Shells for
Homeless Turtles Foundation" or some such. If the organization in
question is likely to be viewed as a worthy cause, that might help. On
the other hand, "a supporter of the Hooters Waitress Harrassers' Legal
Fund" might not look so good.