Kevin Zelnio, a graduate student at Penn State University, and author of the blog The Other 95%: An Appreciation of the Underappreciated Majority of Life, has made available online 3 powerpoint slideshows from his history of science talks here.
Direct links:
Sir Charles Lyell and Geology’s Influence on Darwin’s Theories
Hooker Huxley Haeckel: Darwin’s Apostles
300 Years of Linnaeus!
I also have my powerpoint slides from a paper presentation I did last year on Darwin’s seed experiments available here.
The Dispersal of Darwin 