Not rail trails, but pretty much the same thing are the
Delaware and Raritan Canal Trail, from Brunswick to Trenton, then links to the section along the river up to Frenchtown, NJ, I think it's 70 miles. Gravel surfaced.
The other biggie is the
Erie Canalway Trail system, which spans NY State from Albany to Buffalo, with extensions on assorted canals to Lake Champlain, Oswego, etc.... according the the NY State site -
http://www.ptny.org/canalway/
I know there are more, such as the
Four Seasons Adventure Trail, running 27 miles from Newport, Maine north to Dover-Foxcroft, Maine. Gravel, link -
http://www.nrcm.org/documents/Newpor...Trail_hike.pdf
The
Petit du Nord Trail in Quebec, north of Montreal, 124 miles, rail trail, gravel -
http://en.wikipedia.org/wiki/Parc_Li..._Train_du_Nord
This one is supposed to be a great ride with towns every few miles, great french food for breakfast, lunch and dinners, B&B's, shuttle busses....