This post will be updated with websites that list hikes in the USA.
http://www.wta.org/ hikes, reviews, magazine, interactive trail map for Washington.
http://www.cooltrails.com/ Northwest hiking trail reviews.
http://http//sectionhiker.com/long-distance-hiking-trails/ Long Distance trails in America (plan a week to several months).
http://en.wikipedia.org/wiki/Long-distance_trails_in_the_United_States The title is kind of obvious.
Please comment if you know of other good websites.