Why is rape not in the 10 commandments? Seems like a good one to touch on.

I'm sure there could have been room in there somewhere if he wanted it. Why not?
Note: This answer comes from the perspective of the Old Testament alone, since the question was in regard to the Ten Commandments and gives no indication that it's seeking a &quot;Christian&quot; perspective, but does give indication that it's seeking a historical perspective (since it references the Ten Commandments).
History of the ten Commandments
Why is rape not included among the these commandments?  Because there are many things (including homosexuality, having sex with your fathers wife, not wearing clothes made of both wool and cotton, etc.) that are not in them.
The Ten Commandments were originally written on stone tablets after Moses ascended Mount Sinai.  Their purpose was to provide a set of basic, simple laws that would hold the nation of Israel over until they got the full Levitical law.
The Levitical law was not given until the book of Leviticus, after the Ten Commandments had been given.  These commandments were not meant to be all-encompassing, but simply meant to give them the top-ten basic laws that God wanted the Israelites to obey until they could get the complete Law.
Rape defined
It is important to note that &quot;rape&quot; during those days was not a crime against a woman, but rather a crime against the head of the household (History of Rape).
To understand how rape plays out in the Old Testament, it is important to understand adultery.  Adultery was a sin that had the death-penalty associated with it.

Deuteronomy 22:22 (NIV) 
If a man is found sleeping with another man’s wife, both the man who slept with her and the woman must die. You must purge the evil from Israel.

However, if the man were to rape another man's wife, only the man would die, since he is the one that committed the act of adultery.

Deuteronomy 22:25
But if out in the country a man happens to meet a young woman pledged to be married and rapes her, only the man who has done this shall die.

Note that in Old Testament times, betrothal came after the marriage price had been paid.  The groom and the bride at that point were effectively married, although there was a waiting period before they could live together.
Now, if a man rapes a woman who is not pledged to be married, then he has not committed adultery and did not deserve death.  Instead, he was forced to pay the marriage price, taking the girl/woman as his wife.

Deuteronomy 22:28-29 (NIV)
If a man happens to meet a virgin who is not pledged to be married and rapes her and they are discovered, he shall pay her father fifty shekels of silver. He must marry the young woman, for he has violated her. He can never divorce her as long as he lives

What these laws are showing is that rape is not &quot;non-consensual&quot; sex as we think of it today.  It's actually a crime against the man who &quot;owns&quot; the woman (for lack of a better term).  The crime committed in the case of a betrothed or married girl is the crime of adultery.  The crime committed in the case of a non-betrothed, unwed girl is the crime of not paying for something that you've taken.
The punishment for rape back then was the same as the punishment for either adultery or stealing, based on the marital status of the girl.
This also means... there is nothing in the Old Testament saying that non-consensual sex with your wife is wrong.
Rape as Adultery/Theft
With the definition above, we see that rape carried the punishment of either adultery or theft, based on the marital status of the girl/woman.  With that in mind, the laws of adultery and stealing were in the Ten Commandments:

Exodus 20:14-15
14 You shall not commit adultery.
15 You shall not steal.

If we compare these laws established in the Ten Commandments with the rules established in Deuteronomy, we see that rape was considered either stealing or adultery.
Because of this, the root law that is being violated is actually covered in the these commands.
Summary
Rape, from the Old Testament perspective, is either considered adultery or thievery (based on the marital status of the woman).  Those two root laws are specifically mentioned in the Ten Commandments.  Therefore, the two laws that might be broken from a given rape are actually written there.