Analysis at least two Monologues from Hamlet to highlight his mental state.

Hamlet being a melancholy character and given to obsessive brooding tends to analyse the ramification of his action that outweighs the action while making reflection the action itself.
Following two monologues would put this into perspective:
a) O what a rogue and peasant slave am I........
(--Act II, Scene II; 553-585)
Here Hamlet is embittered for being an inactive dreamer in executing what he thought his duty. He looks upon himself as a coward.
Hamlet reveals through these lines his mental make up: a person not born with the spirit of vengeance and ferocity of anger. His is an intellectual bent of mind that is susceptible to reason and evidence—even in the face of near conviction—rather than the fury of a savage mind.
So he stages a play to rouse his soul from the scruples of feeble irresolution hiding behind morality into passionate commitment to avenging his father’s murder.
He seems always at loggerheads with reason, indecision and sense of duty.
Thus in the words of Coleridge, ‘It is this tragic flaw of inaction that makes Hamlet both a tragedy of reflection and a tragedy of moral idealism.
b) Now might I do it pat, now a is a-praying......
(--Act III, Scene III; 73-95)
Here is another classical example of Hamlet’s irresolute mind.
Hamlet gets a chance to kill Claudius who was on his kneels praying to give up evil deeds or to fight till to the end. Again Hamlet’s Christian mind reasons against killing Claudius in his prayer as not to let him go straight to heaven as this wouldn’t fit to be a just revenge but a reward. He wants to ensure that Claudius go to hell, a place he thinks more commensurate with the person and his evil deeds. But in hindsight Hamlet lost yet another moment to kill his uncle.
Thus we get a feel of a mind that is caught in the whirl of self-torture and multiple volitions.