Currently the Acela does the Philly-NYC run in 1:12. I'm not quite sure I believe the funded improvements (thanks Lex!) will bring that down below an hour, but I suppose it's close enough. Though absent the ARC tunnel (screw you Christie!) or similar, there's still a serious capacity constraint crossing the river into NYC.
...adding that I've only taken the Acela once to NYC. The "normal" service can be as quick as 1:19, but most trains take between 1:25-1:30.
