Here is a map from the NFS of all the national (long distance) trails:  natltrails.pdf

I will expand this page with information on long/medium distance hikes. For now, just the web links:

Applachian Trail: http://www.appalachiantrail.org/site/c.jkLXJ8MQKtH/b.727749/k.91A1/AT_Essentials.htm

International AT: http://www.internationalat.org/Pages/index

Long Trail (VT): http://www.greenmountainclub.org/page.php?id=2

Long Path (NJ/NY): http://www.nynjtc.org/trails/longpath/index.html

Pacific Crest Trail: http://www.fs.fed.us/pct/

John Muir Trail: http://www.pcta.org/about_trail/muir/over.asp

Tahoe Rim Trail: http://tahoerimtrail.org/

Continential Divide Trail: http://www.cdtrail.org/page.php

American Discovery Trail (across US): http://www.discoverytrail.org/

Pacific Northwest Trail:  http://www.pnt.org/

Arizona Trail: http://www.aztrail.org/

North Country Trail: http://www.northcountrytrail.org/

Florida Trail: http://www.floridatrail.org/web/index.php

Colorado Trail: http://www.coloradotrail.org/

Benton Mackaye Trail (GA, TN, NC): http://www.bmta.org/

Mountain-to-Sea Trail (NC): http://www.ncmst.org/

Buckeye Trail (OH): http://www.buckeyetrail.org/

Ice Age Trail (WI): http://www.iceagetrail.org/

Link to US hiking and mountain biking trails: http://www.americantrails.org/resources/statetrails/index.html 

Local Hikes

Mid-State Trail: http://www.midstatetrail.org/

Metacomet-Monadnock Trail: http://amcberkshire.org/mm-trail

Europe:

Camino de Santiago de Compostela: This is a very famous trail running from France to Spain along a religious pilgrimage route. Lots of web material on this, not sure if there is an official site, here is a start: http://www.caminodesantiago.me.uk/

Via Alpina: This looks like a great hike -”Europe’s answer to the AT”: http://www.via-alpina.org/site/