What are some paradoxes and verbal ironies in each act of Othello?

In Act 3, Iago and Othello discuss the possibility of Desdemona's unfaithfulness.  Othello does not believe Iago's claims at this point; however, he is becoming suspicious and worries that the rumor might in fact be true.  Iago tells Othello that Cassio is an honest man:

Men should be what they seem.  Or those that be not, would they might seem none.  (III.iii.124-125)

This is ironic because Iago does not want Othello to believe that Cassio is an honest man--he is simply planting a seed of doubt in Othello's mind.  Further, Iago suggests that a man's true character should be what he shows other people; however, this is certainly not the case for Iago who is scheming under Othello's nose.