Nigel,
Knoll West in Parsippany, New Jersey is fantastic. It's open to the public and not too far out of the way on the route from NYC to Philadelphia. It's a Charles Banks course, so it has a number of the template holes that are discussed on this site regularly. I am relatively new to New Jersey, but Knoll West has the best set of greens I have seen on a public course in this area (maybe any area for that matter).
There are plenty of other public options in New Jersey and Pennsylvania that are not far off of your route that are definitely worth playing.
PM me if you are looking for a game and we can try to meet up.
Ben