Can you add to the Murder-Motive list?

Anyone see Castle last night?

Stephen J. Cannell said there are three reasons for murder:

1.) Money
2.) Love
3.) To cover up a crime

As a mystery writer, I thought through my books and why my people have killed and I came up with a fourth -

REVENGE

I agree that every motive boils down to a limited number of reasons but I don't think REVENGE can be broken down into the list above. I believe REVENGE stands on its own.

What do you think?
Do you think something is missing from the list?
Psychotic behavior doesn't count for the murder myster list.

Ooh - self defense or accidents. Those two stand on their own and could make quite a good murder mystery if the victim-killer covers up the killing for some reason. That reason probably from Stephen J. Cannell's list of three...

Hmmm, self defense and accidents aren't murder, are they?

What can you come up with?