I've stayed at the PHL Airport Marriott, which is EXCELLENT. Very nice rooms, up to date furnishings, excellent sound insulation and cool views of the runway at PHL. It is connected via a short skybridge to the USAirways terminal at PHL.

I'm also familiar with the BOS Hilton, which is only a few years old. I know that the public areas are nice and you can access it via skybridge from all terminals at BOS.