What are good monologues?

Shakespeare

Macbeth:

LADY MACBETH- What beast was't, then,

That made you break this enterprise to me?

When you durst do it, then you were a man;

And, to be more than what you were, you would

Be so much more the man. Nor time nor place

Did then adhere, and yet you would make both:

They have made themselves, and that their fitness now

Does unmake you. I have given suck, and know

How tender 'tis to love the babe that milks me:

I would, while it was smiling in my face,

Have pluck'd my nipple from his boneless gums,

And dash'd the brains out, had I so sworn as you

Have done to this

A Midsummer Nights Dream:

HELENA- O spite! O hell! I see you all are bent

To set against me for your merriment:

If you we re civil and knew courtesy,

You would not do me thus much injury.

Can you not hate me, as I know you do,

But you must join in souls to mock me too?

If you were men, as men you are in show,

You would not use a gentle lady so;

To vow, and swear, and superpraise my parts,

When I am sure you hate me with your hearts.

You both are rivals, and love Hermia;

And now both rivals, to mock Helena:

A trim exploit, a manly enterprise,

To conjure tears up in a poor maid's eyes

With your derision! none of noble sort

Would so offend a virgin, and extort

A poor soul's patience, all to make you sport.

Contemporary

Crimes of the Heart:

Monologue where Babe talks to Meg about how she killed her husband.

One of Shakespeare's best monologues is 'Puck's Monologue' from A Midsummer Night's Dream.

Puck:

If we shadows have offended,

Think but this, and all is mended;

That you have but slumbered here

Whilst these visions did appear.

And this weak and idle theme,

No more yielding but a dream,

Gentles, do not reprehend;

If you pardon, we will mend.

And, as I am an honest Puck,

If we have unearned luck

Now to 'scape the serpent's tongue,

We will make amends, ere long,

Else, the Puck a liar call.

So, goodnight unto you all!

Give me your hands, if we be friends,

And Robin shall restore amends.

Hope it is long enough- it is an incredibly famous extract. Good luck!