At the beginning of the play, Macbeth is a man of honor. He bravely enters the battle against Macdonwald and others, risking his life in service of his king. That, in itself, is an honorable deed, as reported by a sergeant who had just returned from the scene of battle:
For brave Macbeth--well he deserves that name--
Disdaining fortune, with his brandish'd steel,
Which smoked with bloody execution,
Like valour's minion carved out his passage
Till he faced the slave;
valiant cousin! worthy gentleman!
It is clear that Macbeth is respected and much admired at this point. He is truly a man of honor. Things quickly go awry for Macbeth when, driven by "vaulting ambition", he commits the foulest of deeds: murdering his king after having heard the witches' predictions and believing them. From hereon, everything changes and Macbeth loses all the honor he once so richly possessed and deserved.
King Duncan is a man of honor and Macbeth admits as much when he expresses doubt about assassinating him:
Besides, this Duncan
Hath borne his faculties so meek, hath been
So clear in his great office, that his virtues
Will plead like angels, trumpet-tongued, against
The deep damnation of his taking-off;
Macbeth expresses fear that since king Duncan is such an honorable man that the outcry against his murder will be much greater than it would have otherwise been and that the clamor for revenge would therefore will be much stronger.
Clearly, Banquo is also a man of honor and Macbeth expresses fear of his noble qualities:
Our fears in Banquo
Stick deep; and in his royalty of nature
Reigns that which would be fear'd: 'tis much he dares;
And, to that dauntless temper of his mind,
He hath a wisdom that doth guide his valour
To act in safety. There is none but he
Whose being I do fear: and, under him,
My Genius is rebuked;
At this point, Banquo is Macbeth's greatest threat and he then plots to have him killed later.
There are many other similar examples of men of honor throughout the play. We know that Macduff is well-respected, so too Malcolm and king Edward of England, who is practically regarded as a saint. So too do we have Siward, who led Malcolm's troops into battle and his son, the young Siward, who died valiantly when he challenged Macbeth.
I believe that a more appropriate topic would be to show the "lack of honor" in Macbeth. There are far many more examples which show behavior which is not honorable: the murders, poisonings, and belief in the witches' premonitions.
But, if forced to, I agree with post #2- you could not look at Macbeth; you would, instead, need to look at other characters like Banquo.
To talk about honor in the positive sense, I think you'd have to talk about Macduff or Malcolm. Both of these men display honor because they will not give in to Macbeth. Macduff displays honor when he is so anguished at finding out that Malcolm seems to be no better than Macbeth. Malcolm shows honor by being so adamant about how a king should behave. These two men can be directly contrasted with Macbeth who has so much ambition and so little honor.