PS -- for travel from NYC south, I have found that I can get to my destination FASTER by taking the Amtrak Metroliner to Philadelphia, and flying out of PHL, than taking a cab at rush hour to LGA, JFK or EWR.

Penn Station is in Mid-town Manhattan. The Metroliner gets to downtown Philadelphia just as fast as a cab gets to LGA (1hr 10 min), if you consider that you will likely stand in the cab line for 20 minutes at 5:00p or 6:00p in NYC.

Philadelphia has a very efficient local rail system that takes you to the airport every 30 minutes on a 20 minute trip.

Also, PHL is usually not delayed as LGA is often due to air traffic control problems.

Just a thought...