The last row of many Acela cars is a single seat, with tons of room in front of you. There's not a bad seat on Acela but this one is a cut above. As you might imagine, it's usually the first seat to go. The best way to get the seat: have a bellcap carry your bags to the train. In Boston and New York, they'll take you to the train before general boarding begins. You tip them $2-5 and voila, the best seat on the train. I sometimes get funny looks from fellow passengers who think "what's such a healthy looking guy doing have the bellcap carry his bags for him." Then they see me sitting in this seat and think "pretty smart (or obnoxious) guy."
This one qualifies as the greatest bargain in travel. $15 for your first bag on American or $2 for the best seat on Acela. Not much competition.