Trying to post something useful since this is the 1,000,000 post!
ADT-American Discovery Trail-6800miles-http://www.discoverytrail.org/
AT-Appalachian Trail-2179.1miles-http://www.appalachiantrail.org -- (corrected for 2010 mileage 8/15/10)
AT-Arizona Trail-790miles-http://www.aztrail.org/
AT-Allegheny Trail-330miles-http://www.aldha.org/alleghen.htm
BART-Bay Area Ridge Trail-500miles-http://www.ridgetrail.org/
BMT-Benton MacKaye Trail-300miles-http://www.bmta.org/
BST-Bonneville Shoreline Trail-90miles-http://www.bonnevilleshorelinetrail.org/
BT-Baker Trail-141miles-http://www.dcnr.state.pa.us/forestry/hiking/baker.aspx
BT-Buckeye Trail-1444miles-http://www.buckeyetrail.org/index.html
CDT-Continental Divide Trail-3100miles-http://cdtrail.org/page.php
CH-Cohos Trail-156miles-http://www.cohostrail.org
CLT-Chief Ladiga Trail-33miles-http://epic.jsu.edu/clt/
COCT-C&O Canal Trail-184.5miles-http://bikewashington.org/canal/
CT-Colorado Trail-(478-500)miles-http://www.coloradotrail.org/
CT-Cumberland Trail-300miles-http://www.cumberlandtrail.org/
CT-Chilkoot Trail-33miles-http://www.nps.gov/klgo/planyourvisit/chilkoottrail.htm
DRT-Duncan Ridge Trail-35miles-http://georgiatrails.com/trails/duncan.html
ECG-East Coast Greenway-3000miles-http://www.greenway.org/
ECT-Eastern Continental Trail-5400miles-http://www.nimblewillnomad.com/easte...rail_guide.htm
FLT-Finger Lakes Trail-562miles-http://www.fingerlakestrail.org/
FT-Florida Trail-1400miles-http://www.floridatrail.org/
FT-Foothills Trail-76miles-http://www.foothillstrail.org/
GAP-Great Allegheny Passage-318miles-http://www.atatrail.org/
GET-Grand Enchantment Trail-730miles-http://www.simblissity.net/grand_enchantment.shtml
GWL-Great Western Loop-6875miles-http://www.andrewskurka.com/GWL/abou...escription.php
GWT-Great Western Trail-4455miles-http://gwt.org/
HLC-High Line Canal-60miles-http://www.douglas.co.us/openspace/H...nal_Trail.html
HST-Horse Shoe Trail-140miles-http://hstrail.org/
HST-High Sierra Trail-61miles-http://www.nps.gov/seki/planyourvisi...erra-trail.htm
HT-Hayduke Trail-800miles-http://hayduketrail.org/ -- (added 8/13/10)
HT-Highlands Trail-150miles-http://www.highlands-trail.org/
IAT-Ice Age Trail-1000miles-http://www.iceagetrail.org/
IAT-International Appalachian Trail-1900miles-http://www.internationalat.org/
JMT-John Muir Trail-211miles-http://johnmuirtrail.org/
KT-Katy Trail-185miles-http://www.great-trails.com/katy.shtml
KT-Knobstone Trail-58miles-http://www.indianatrails.com/content...e-hiking-trail
LHHT-Laurel Highlands Hiking Trail-70miles-http://www.dcnr.state.pa.us/Forestry/hiking/laurel.aspx
LP-Long Path-350miles-http://www.nynjtc.org/region/long-path
LSHT-Lone Star Hiking Trail-129miles-http://www.fs.fed.us/r8/texas/recrea...arhiking.shtml
LT-Long Trail-273miles-http://www.greenmountainclub.org/page.php?id=2 -- (corrected for 2010 mileage 8/15/10)
MDHT-Maah Daah Hey Trail-97miles-http://www.mdhta.com/info.htm
MDT-Mason-Dixon Trail-193miles-http://www.masondixontrail.org/
MMT-Metacomet-Monadnock Trail-114miles-http://amcberkshire.org/mm-trail
MRHT-Michigan Rider & Hiker Trail-220miles-http://members.tm.net/trailrider/pub...ore_trail.html
MSG-Monadnock-Sunapee Greenway-50miles-http://www.msgtc.org/
MSST-Michigan Shore-to-Shore Trail-220miles-http://members.tm.net/trailrider/pub...ore_trail.html
MST-Mountains-to-Sea Trail-961.8miles-http://www.ncmst.org/map.html
MST-Midstate Trail (PA)-313miles-http://www.hike-mst.org/ -- (added 8/15/10)
MT-Midstate Trai (MA)l-92miles-http://www.midstatetrail.org/
MT-Mattabesett Trail-57miles-http://en.wikipedia.org/wiki/Mattabesett_Trail
NCT-North Country Trail-4600miles-http://www.northcountrytrail.org
NPNHT-Nez Perce National Historic Trail-1170miles-http://www.fs.fed.us/npnht/plan/decisionnotice.shtml
NPT-northville-Placid Trail-133miles-http://www.aldha.org/northvil.htm
NTT-Natchez Trace Trail-65miles-http://www.nps.gov/natt/index.htm
OCT-Oregon Coast Trail-382miles-http://visittheoregoncoast.com/2009/...-hiking-guide/
OHT-Ozark Highlands Trail-165miles-http://www.hikearkansas.com/ohta.html
OT-Ozark Trail-140miles-http://www.ozarktrail.com/
PCT-Pacific Crest Trail-2654miles-http://www.pcta.org/
PNT-Pacific Northwest Trail-1200miles-http://www.pnt.org/
PT-Palmetto Trail-425miles-http://www.sctrails.net/TRAILS/ALLTR...O%20TRAIL.html
PT-Pinhoti Trail-295miles-http://www.pinhotitrailalliance.org/index.html
RFT-Robert Frost Trail-47miles-http://en.wikipedia.org/wiki/Robert_...ssachusetts%29
R2R-Rim to Rim, Grand Canyon-23.5miles-http://www.zionnational-park.com/rim-to-rim-grand.htm -- (added 8/13/10)
R2R-River to River Trail, Southern Illinois-(160-176)miles-http://www.rivertorivertrail.com/home.html -- (added 8/13/10)
STT-Sheltowee Trace Trail-282miles-http://www.sheltoweetrace.com/
SHT-Superior Hiking Trail-205miles-http://www.shta.org/
SRKG-Sunapee-Ragged-Kearsarge Greenway-75miles-http://www.srkg.com/
SST-Skyline-to-the-Sea Trail-29miles-http://en.wikipedia.org/wiki/Skyline-to-the-Sea_Trail
ST-Susquehannock Trail-85miles-http://www.dcnr.state.pa.us/FORESTRY...uehannock.aspx
TRT-Tahoe Rim Trail-165miles-http://www.tahoerimtrail.org/index.p...d=78&Itemid=51
TT-Tuscarora Trail-250miles-http://www.dcnr.state.pa.us/FORESTRY...tuscarora.aspx
VCT-Virginia Creeper Trail-35miles-http://www.vacreepertrail.com/
WT-Wonderland Trail-93miles-http://www.nps.gov/mora/planyourvisi...land-trail.htm