Getting ready to sell my M9700. What steps should I take to ensure all of my personal info is gone?

I would appreciate suggestions on what to leave on the computer (i.e. Win 7, any other programs), but more importantly what to remove. I want to be sure there is no trace of me, or my identity left on it when it leaves my hands.

What do you all do if and when you sell?

Thanks in advance for your suggestions!