Amtrak is offering 20% off on service to Philadelphia. In reality, the discount applies to all Northeast Corridor trains, though Metroliner and Acela Express are as usual excluded.
Discount code V735 is valid on tickets purchased through April 22, 2006 for travel through April 25, 2006. Blackout dates are: November 22-29, 2005; Dec 16-Jan 2, 2006; Jan 13-16, 2006; Feb 17-20, 2006; April 13-17, 2006.
On itineraries where V735 is not available, try H542. It’s a 15% discount that seems to work on most trips, including Metroliner and Acela Express. It’s only valid through December 15.