I don't leave my laptop alone, period. If I go to the bathroom, I take it with me. If I get up to order food, unless I can keep constant eye contact with it I'll take it with me.
Keep in mind that most laptop locks are easily and quickly defeated, and the insurance that comes with the lock is so limited that they rarely pay out (you have to be able to return the lock or lock pieces, and if no damage or evidence of unauthorized opening can be found they won't pay - sucks if the thief steals the lock as well, or picks the lock since it doesn't always leave discernible marks).
So, yeah, I can't recommend any locks.