There are aircraft parking areas all around the airport. Get permission at an air service office near any lot to walk around. A regional commercial airport, Stewart, in Newburgh, N.Y., is easy to get to and easy to park at. At Westchester County Airport, off I-684 in White Plains, there are also commercial passenger jets as well as smaller planes and the viewing is from the new terminal there. For more fun, pick up an inexpensive aircraft-band radio at Radio Shack and listen to the pilot and tower chatter.
Frequencies are easy to figure out by tuning around the band for loud signals.