Macbeth seems to speak most of the famous lines from this play, and most of them express some kind of regret or reflection about the brevity and futility of life. This is one of those from Act V, scene v:
Tomorrow, and tomorrow, and tomorrow
Creeps in this petty pace from day to day
To the last syllable of recorded time;
And all our yesterdays have lighted fools
The way to dusty death.
Another one I like is a little more frivolous and is spoken by the Second Witch in Act IV scene i:
By the pricking of my thumbs, something wicked this way comes.
This is spoken about Macbeth, and it is a sensing of evil before it arrives. We often think about getting a cold chill or goosebumps or the hair on our arms and/or the back of our necks standing on end--a pretty universal experience in human nature.
I would suggest Banqo's warning to Macbeth in Act I scene iii
And oftentimes, to win us to our harm,
The instruments of darkness tell us truths,
Win us with honest trifles, to betray's
In deepest consequence—
and Lady Macbeth's assertion of her husband's humanity which has prevented him from earlier success-
Yet do I fear thy nature;
It is too full o’ the milk of human kindness
To catch the nearest way. Thou wouldst be great;
Art not without ambition, but without
The illness should attend it.