I love the point you just made: "monologues generally come from an elevated state of emotion". This is so true because people tend to curse more when they are upset...but also because I feel the most effective monologues are more emotion-driven then exposition-driven.

Sure...they are a way to feed the audience more information...but they feel so much more vital and natural when they come from a place of pain, anguish, passion, or love.

Even quiet introverted people will rattle off a long-winded statement in real life to defend themselves or express frustration. So I feel audiences are also more likely to except monologues if they see a character REALLY SPEAKING FROM THE HEART.

It is the pitch-perfect, verbally poetic monologues that come off as phony, over the top, and boring...because they don't sound like the first thing that would have spewed out of that person's mouth during an emotional moment - they sound like they were proof-read and polished by an editor from The New York TImes.

Even when we are mad, sad, or extremely glad...the words never some out perfect. I believe that clever articulation is where most monologues fail. Sorry for my own long-winded monologue right here...lol. Thanks Scott for another informative post!

I think the most relevant point was already made. "An elevated state of emotion."
A quiet emotional moment can justify a monologue. You can dish out some exposition or
internal conflict without being on-the-nose or preachy. But you have to build up for that moment,
have to earn it. Or it can be a moment where two characters argue with each other, one wins the
upper hand and is therefore able to throw all her built-up emotions toward her opposition.

I know suggestions are over but I like to mention a monologue in 'The Fisher King':

http://www.youtube.com/watch?v=wN3bcE7ldHg&feature=related

Parry: It begins with the king as a boy, having to spend the night alone in the forest to prove his
courage so he can become king. Now while he is spending the night alone he's visited by a sacred
vision. Out of the fire appears the holy grail, symbol of God's divine grace. And a voice said to the
boy, "You shall be keeper of the grail so that it may heal the hearts of men." But the boy was blinded
by greater visions of a life filled with power and glory and beauty. And in this state of radical
amazement he felt for a brief moment not like a boy, but invincible, like God, so he reached into the
fire to take the grail, and the grail vanished, leaving him with his hand in the fire to be terribly
wounded. Now as this boy grew older, his wound grew deeper. Until one day, life for him lost its
reason. He had no faith in any man, not even himself. He couldn't love or feel loved. He was sick
with experience. He began to die. One day a fool wandered into the castle and found the king alone.
And being a fool, he was simple minded, he didn't see a king. He only saw a man alone and in pain.
And he asked the king, "What ails you friend?"...

Jack is the Fisher King and Parry is the fool who saves him without knowing it and without knowing
that Jack's actions led to him becoming that 'fool'. It is Parry's monologue but it is more about
Jack's emotions being reflected in the story Parry tells him. It conveyes Parry's (extrinsic) goal
but at the same time Jack's (intrinsic) need. It is a beautiful moment and loaded with emotion,
hidden exposition and the film's title. So it's better gotta be good, and it definitely is.