NYC is great for spotting, after all!
If you like Business Aircraft you should go to TEB Teterboro (Bus from 42nd Street!). Great action and lot's of impressive stuff!
isn't too easy, you can see the Concorde from the BA
Terminal and often the AF
Concorde in front of the International Terminal parked. You can also take the bus to the famous "Customs Building" where a lot of A.net shot's were taken. It takes a while to get there and I can't remember the Bus # to take. Maybe somebody else can help...
isn't too bad, especially if they approach over Queens. Then you should take a bus to the "Academy of Aeronautics" (???) which is just short of one runway. They also have a nice 'tower' where you have a nice view of the action and get live ATC. You just have to find the entrance to the College and ask for the tower.
There are also some spots in the Terminals at LGA
where you can spot a little bit, but not too impressive!
I don't know too much about good spots at EWR