U.S. Presidents of the Twentieth Century This contains sound files of the last 20 Presidents. It is offered by the Vincent Voice Library at Michigan State University. Just select a President and listen.
From the site:
The Voices of American Presidents have been captured by audio pioneers since the early days of sound recording. The invention of Edison's phonograph ushered in a new era of "recorded" history, beginning with President Benjamin Harrison in the late nineteenth century to the present day Bush Administration. The MSU Vincent Voice Library is working to preserve over 100 years of historical spoken word recordings like those of the U.S. Presidents, and is pleased to share these sound samples from its collection.