If you have some time, watch this video by Robert O'Toole. The Nature Photographers of the Pacific Northwest (NPPNW) invited Robert to present to us a year or two ago. I think his information and presentation style is better than many of the big names. We've had folks like Art Wolfe, George Lepp, Rod Planck, and Frans Lanting, but I have learned more from Robert than any of the others.
Edit: Here's another presentation from Robert.
Edit: Here's another presentation from Robert.