As central as The Prophecy of the Chosen One is to the Star Wars Saga, truth be known, we have very little idea as to its actual contents.

What do we actually know? Let's take a look at the central times the Prophecy has been referred to...

The earliest reference to what could be the Prophecy actually appears in the 3rd draft of the script to the original Star Wars film, Episode IV, dated August 1, 1975:

"... and in the time of greatest despair,
there shall come a savior, and he shall
be known as
The Son of The Suns."
Journal of the Whills, 3:127

Whether this is official or not is completely contestable. Also debatable is, if this is canon, whether it has anything at all to do with the Prophecy of the Chosen One.

It should be noted, however, that some fans claim a Gungan can be heard yelling, "The son of suns!" during the end celebration of Return of the Jedi in the DVD version of the Original Trilogy.

If this is a piece of the Prophecy, how does it fit in? "The Son of The Suns" seems to have two equally valid and possibly coinciding interpretations:

1) The Son of The Suns refers to one born on Tatooine, i.e. born under a planet with multiple suns.

2) The Son of The Suns refers to one born of the galaxy, i.e. has no natural birth father.

It is now time to tread into more canonical ground. Let's kick it off as early chronologically as we can go, with Episode I (all quotes following taken from movie scripts):

YODA : Master Qui-Gon more to say have you?
QUI-GON : With your permission, my Master. I have encountered a vergence in the Force.

Now, we need to define the word "vergence." Dictionary.com reports:

1. A measure of the convergence or divergence of a pair of light rays, defined as the reciprocal of the distance between a point of reference and the point at which the rays intersect.

2. The inward or outward turning of one or both eyes that occurs when focusing on an object.
...
A disjunctive movement of the eyes in which the fixation axes are not parallel.

Helpful...

I admit, the above definitions seem difficult to grasp. But the conclusion I'm drawing is, vergence means an unequal focus. In the context of Star Wars, we're looking at an unequal focus in the Force. Perhaps an overmanifestation where there is no reason for it to be.

YODA : A vergence, you say?
MACE WINDU : Located around a person?

Notice Master Windu automatically assumes our overmanifestation is present in a person, not a place.

QUI-GON : A boy... his cells have the highest concentration of midi-chlorians I have seen in a life form. It is possible he was conceived
by the midi-chlorians.
MACE WINDU : You're referring to the prophesy of the one who will bring
balance to the Force... you believe it's this boy??

Apparently, "vergence" is the word Qui-Gon has chosen to describe a person with an incredibly high concentration of midichlorians. High enough that he feels safe drawing the conclusion he was conceived by the midichlorians.

Mace's response shows that this assumption is an automatic correlation to the Prophecy. Also notice that he refers to the Prophecy as one telling of a person who will bring balance to the Force.

So what we know about the Prophecy is:

1) It tells of an individual conceived by midichlorians
2) This individual will bring balance to the Force

QUI-GON : I don't presume...
YODA : But you do! Revealed your opinion is.
QUI-GON : I request the boy be tested.

The JEDI all look to one another. They nod and turn back to OBI-WAN and
QUI-GON.

YODA : Trained as a Jedi, you request for him?
QUI-GON : Finding him was the will of the Force...I have no doubt of that.
There is too much happening here...
MACE WINDU : Bring him before us, then.
YODA : Tested he will be.

The Jedi seem afraid of the Chosen One. Rather than eagerly anticipating the testing of the one who could bring balance to the Force, the Jedi seem leery of this individual.

It's possible this is simply Jedi scepticism at Qui-Gon's words. Perhaps the Prophecy contains information (i.e. the fall of the Jedi Order) that would scare the Jedi.

Most likely, the Prophecy contains some trying times, such as the re-emergence of the Sith or a period of darkness, that the Jedi would prefer not to experience. Perhaps it's simply they don't like the idea of the Force being imbalanced.

The Prophecy says:
1) An individual will be conceived by midichlorians
2) This individual will bring balance to the Force
3) Something about the Prophecy makes the Jedi nervous

Later in The Phantom Menace:

MACE WINDU : He is too old. There is already too much anger in him.
QUI-GON : He is the chosen one... you must see it.
YODA : Clouded, this boy's future is. Masked by his youth.

The Council seems clearly against Anakin's training. Ironic that they would cite his youthfulness as masking his future, since the usual Jedi hopefuls are much younger.

And notice Qui-Gon assumes that proving that Anakin is the Chosen One would convince the Council that he must be trained. However, even though the Council does not deny this possibility, they still hesitate to train Anakin.

Still later:

QUI-GON : He is the chosen one...he will...bring balance...train him!

A re-instatement that the Chosen One will bring balance to the Force.

Still onward:

YODA : The Chosen One the boy may be; nevertheless, grave danger I fear in his training.

Is Yoda hoping to deter Obi-Wan from training Anakin, despite the admittance that he may be the Chosen One?

Alright, we made it through Episode I! Now, for Attack of the Clones. Only thing here is:

OBI-WAN: I am concerned for my Padawan. He is not ready to be on his own.
YODA: The Council is confident in this decision, Obi-Wan.
MACE: He has exceptional skills. The Council is confident in its decision, Obi-Wan. If the prophecy is true, he will be the one to bring balance to the Force.

This is super-important: Mace says if the Prophecy is true, then Anakin will bring balance to the Force. NOT if Anakin is the Chosen One, then he will bring balance to the Force.

You see, Mace does not seem to doubt that Anakin is the Chosen One; the doubt is expressed as to whether the Prophecy itself is true.

The Prophecy says:
1) An individual, the Chosen One, will be conceived by midichlorians
2) The Chosen One will bring balance to the Force
3) Something about the Prophecy makes the Jedi nervous
4) Anakin fits the description of the Chosen One
5) The Prophecy may or may not be true

That's it for Episode II. Now to Revenge of the Sith:

OBI-WAN: With all due respect, Master, is he not the Chosen One? Is he not to destroy the Sith and bring balance to the Force?
MACE: So the prophecy says.
YODA: A prophecy . . . that misread could have been.

Oh, great. So in other words, everything you thought you knew could be wrong.

Still, the Jedi are not denying that Anakin is the Chosen One. Also, they tie balancing the Force to destroying the Sith, which could be the cause of the Jedi's earlier nervousness regarding the appearance of the Chosen One.

The Prophecy says:
1) An individual, the Chosen One, will be conceived by midichlorians
2) The Chosen One will bring balance to the Force
3) Something about the Prophecy makes the Jedi nervous
4) Anakin fits the description of the Chosen One
5) The Prophecy may or may not be true
6) The Prophecy may or may not be interpreted correctly
7) The Prophecy says the Force will be balanced with the destruction of the Sith

And lastly:

OBI-WAN: You were the Chosen One! It was said that you would destroy the Sith, not join them. It was you who would bring balance to the Force, not leave it in Darkness.

Obi-Wan reaffirms that the Sith are to be destroyed and the Force balanced by the Chosen One.

So, organized, what we know of the Prophecy:

1) The Prophecy says an individual, the Chosen One, will be conceived by midichlorians
2) The Prophecy says the Chosen One will bring balance to the Force
3) The Prophecy says the Force will be balanced with the destruction of the Sith
4) Anakin fits the description of the Chosen One
5) Something about the Prophecy makes the Jedi nervous
6) The Prophecy may or may not be interpreted correctly
7) The Prophecy may or may not be true

As a footnote to this whole thing, Wookieepedia has an interesting page on the Sith'ari, apparently a prophesied being from the Knights of the Old Republic games.