If you mean spotting as in logging tail numbers, there is an observation lounge in the terminal. To the right of the food court, overlooks the ramp and the main runway. It's the designated smoking area if that would be a problem for you.
If you mean spotting as in shooting photos, the lounge would mean shooting through glass. To the right of the terminal there is a small area which overlooks the US Express gates and some taxying shots of other traffic is possible. Don't know how long you'll be left alone there before the arrival of the screwity goons though