Hamlet speaks several important soliloquies in William Shakespeare's play "Hamlet," each of which reveal important information about his state of mind.
"O, that this too too solid flesh would melt" Act 1, Scene 2
This soliloquy reveals Hamlet's despair at the news that his mother Gertrude will be marrying Claudius, his father's brother and murderer. As with "to be or not to be", it touches on the theme of suicide, of Hamlet thinking his position in life is so terrible that it would be better not to exist.
"O, what a rogue and peasant slave am I!" Act 2 Scene 2
This soliloquy is spoken after Hamlet sees the players performing a scene adapted from Virgil's Aeneid. In the soliloquy, he contrasts acting with reality. Both actors in plays and Hamlet himself need to hide their real feelings and play a part. This touches on the "play within a play" and surface versus reality themes.
"To be, or not to be? That is the question—" Act 3, Scene 1
In this famous soliloquy, Hamlet is experiencing despair, and thinking about committing suicide. He is pretending to be mad, as part of his plot against Claudius, and as part of this pretense has rejected Ophelia, causing her great pain. He is anticipating the plot he will organize with the players to assure himself of Claudius' guilt, which if it succeeds, will lead to him having to murder Claudius to avenge his father. The main themes addressed in this soliloquy are despair, suicide, and madness.