I have just written a hubpage on the best public speakers in the world - my top 10. As I said on the page, watching these speakers on Youtube is like getting free public speaking lessons! My hubpage details my reasoning for each one making the list so I won't repeat it here but suffice to say they are all inspirational, motivating speakers who offer something different.
Who would you rate as a great public speaker? Have a look at my list here: great public speakers