Lectures are available on a variety of general and specific topics.  
Some general headings include:

Ancient Art and Architecture
Medieval Art and Architecture
World Art:  Aboriginal, Early China, Early India, Early Islam
Renaissance Art and Architecture (Individual presentations on Leonardo, Michelangelo, and Raphael available)
American Art and Architecture
Selected artists and Architects from Baroque, 19th Century and 20th Century
Greatest Hits of the Metropolitan Museum of Art
Greatest Hits of the Museum of Modern Art

For more information, email me.