Between Washington, New York, and Boston, Amtrak offers two distinct services: Northeast Regional and Acela Express.
Acela Express service began in late 2000 using brand-new equipment designed for higher speed service. The appearance of the trains is similar to that of some European high-speed trains. Classes of service include business class and first class, and among other features, these trains offer "Quiet Cars" (cars where use of cell-phones, loud conversations, and other noisy nuisances are not allowed) as well as free wi-fi.
These trains reach 150 mph (240 kph) on a stretch of track between New York and Boston, but mostly run at lower speeds than that. Wikipedia has an excellent page about Acela Express.
Acela Express is Amtrak’s flagship operation in the Northeast and gives a taste of what would be possible if the United States ever got off its rear end and caught up with the rest of the developed world, not to mention Taiwan, China, and South Korea. Fat chance, considering the dreary politics of "no taxes"/disinvestment that mark this era.
KEYSTONE (New York-Philadelphia-Harrisburg)
Keystone service connects Harrisburg, the capital of Pennsylvania with Philadelphia, and points north as far as New York. Only coach service is offered, without any other amenities such as meal or beverage service.
Between Harrisburg and Pennsylvania the service is unreserved like a commuter train.
Between Harrisburg and points beyond Philadelphia seats are reserved, but not preassigned. Trains operate all day long.
Because Downeaster service leaves from Boston North Station and all other Amtrak service operates from South Station, you're best off using a taxi to get between the two stations (instead of transit) if you have much luggage.
CAROLINIAN / PIEDMONT (Charlotte-Raleigh-New York)
ADIRONDACK (New York-Albany-Montréal)
ETHAN ALLEN EXPRESS (New York - Albany - Rutland, Vt.)
VERMONTER (New York-Montpelier-St. Albans, Vt.)
While this is a daytime train, its predecessor along the same route was the Montrealer, an overnight train I took twice in the 90s as far as Montpelier.
EMPIRE SERVICE (New York-Albany-Syracuse-Rochester-Buffalo-Niagara Falls)
MAPLE LEAF (New York-Toronto)
Empire Service (as in the "Empire State") is offered from New York City to Albany and beyond to upstate New York as far as Buffalo and Niagara Falls.
Currently twelve daily trains operate as far as Albany (including the Adirondack that continues to Montreal), and three of those trains continue as far as Buffalo and Niagara Falls. Except for the Adirondack, the trains all offer both coach and business class service.
The Maple Leaf is one of the three trains to Niagara Falls, N.Y., but it continues on to cross the Canadian border and terminate in Toronto, Ontario. It is one of three Amtrak trains that operate internationally, the others being the Adirondack and the trains in the Pacific Northwest that serve Vancouver, B.C. Unlike these other two services where Amtrak personnel work all the way through to Canada, on the Maple Leaf the Amtrak crew is replaced at the Canadian border by employees of VIA Rail Canada, and vice-versa when operating from Toronto to New York.
Amtrak Service and Fares - navigational links
Backward to Routes - Long-distance trains - Eastern (Chicago to the east coast)
Forward to Routes - # 6 - Short-distance corridors - Central