I think that the rhetorical device used the most in the speech would be the presence of anaphora with the refrain "Yes, we can." Obama deliberately ensures that this phrase is repeated, doubled and even tripled back for the listener to fully grasp the positive message emerging from both his speech and campaign for President. We also see the use of antithesis in how Obama juxtaposes his campaign with the current state of affairs in American politics. Consider the discussion of "The Status Quo" and what that present system represents with the vision he is offering. It is at this point where Obama uses some level of aporia, trying to raise doubt in the mind of the listener when he lists the challenges that he and his followers are "up against." In trying to create this sense of doubt, Obama rhetorically creates the basis for "Yes, we can" in that this doubt can be overcome, these fears eradicated. Finally, the climax of the speech is best seen in the ending of "Yes we can" converging with the idea of hope, almost to make the link of "Yes, we can hope." It is a powerful ending to a powerful speech.
thank you! :D