You can browse a list of over 1000 photographers in the Biography database Biography in Context. Not all photographers have works exhibited, but it is a good way to get a sense of who you might find interesting.
To see a list of photographers:
Presidential Debate - President Barak Obama and Republican Candidate Mitt Romney (4 Oct. 2012). Wikimedia Foundation. Denver, CO. Retrieved from https://commons.wikimedia.org.
Google Images is a great tool to see the work of many photographers. For your presentations, however, the images may not be high enough resolution to project well. It's possible to find useful images with introductory information, and sometimes theycome with little or no use restrictions, so give it a try!
Fig.2. William Eggleston. Huntsville, Alabama. Metropolitan Museum of Art. 1970. Web. 11 April, 2012.