I like Obama at personal and political levels, but I think his speech delivery is wooden. Even when he is being emotional, it comes off to me as being too controlled.
Of the presidents that I have heard, Kennedy and Clinton were great speakers. Reagan might have also been a great speaker, but my dislike of him kept me from appreciating any oratory skills he might have had. All the rest were pretty awful – LBJ, Nixon, Ford, Carter and the Bushes. Ford had one great line, which he delivered perfectly. “I am a Ford, not a Lincoln.” Pretty much said it all.