How do make it so people can't see who is on your friend's list over at Facebook?

Click on Account, then Privacy Preferences.

Under “connecting on Facebook”, click on “view settings”. The fourth option down is your friends list. Change the setting there to be whatever you want

If you go to Account in the top right, then Privacy Preferences, you should be brought to a list titled Sharing on Facebook. Click above that on View Settings under Connecting on Facebook, and your Friends List is one of the options to change to Only Me.

And @MrItty is a faster typist than I.

Thanks.